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PKESKNTI-;]) UY 



THE MODERN 



ASPHALT PAVEMENT 



BY 



CLIFFORD RICHARDSON 

n 

M. Am. Soc. C.E., F.C.S. 
Consulting Engineer 



SECOND EDITION, REVISED AND ENLARGED 

FOURTH THOUSAND 



NEW YORK 

JOHN WILEY & SONS, Inc. 

London: CHAPMAN & HALL, Limited 
1914 



TEzio 

7R5 3 



Copyright, 1905, 1908. 

BY 

CLIFFORD RICHARDSON 

Gift 



fcOAXoyJ (Us^tMr ?&. 



MAY 22 1916 



f(H*7fe7 



THE SCIENTIFIC PRESS 

ROBERT DRUMMOND AND COMPANY 

BROOKLYN, N. Y. 



* 



<h 



r 



PREFACE TO FIRST EDITION. 



The present work being designed for a rather wide class of 
readers necessarily includes a large collection of data in regard 
to the chemistry of asphalt and the technology of the industry, 
which is of interest only to civil engineers, asphalt experts and 
those who have made a special study of the subject. The general 
reader is recommended to omit Chapters III to VIII, XII, and 
most of XVI, or to confine his attention to the resumes of them 
which are presented at the end of each. The property holder and 
taxpayer will find the conclusions which will prove of most interest 
to him in Chapters I, II, and XIV, Summaries of III, XIII, XVI, 
and XVII to XXIV 1 relating to the construction of pavements and 
the causes of their deterioration. The relative merits of various 
asphalts for paving purposes are given in a compact form at the 
• end of Chapter XIV. The importance of the action of water on 
asphalt in Chapter XXIII 2 The resume at the end of each Chapter 
will generally furnish the reader at a glance with an opportunity 
of determining whether the details in that Chapter appeal to his 
interest and intelligence. 

The Author. 
New York, February 18, 1905. 

1 Second Edition, Chapter XXV. 2 Second Edition, Chapter XXIV. 

iii 



PREFACE TO SECOND EDITION. 



The very flattering reception given to the first edition of 
this work, resulting in an exceedingly large sale within the last 
three years, has pointed to the very general interest in the 
subject treated of, by the persons for whom the book was 
especially intended. In consequence of the very considerable 
developments in the industry, it has seemed desirable, after the 
exhaustion of the second impression of the first edition, to revise 
the manuscript completely, and to bring it up to date. This has 
been done with the results given in the accompanying pages. 

The writer is indebted to Mr. C. N. Forrest for a revision of the 
matter regarding the methods of analysis which are described, 
and for many other suggestions. 



TABLE OF CONTENTS. 



PAGE 

Introduction 1 



PART I. 

THE FOUNDATION AND INTERMEDIATE COURSE. 

CHAPTER 

I. The Foundation or Base 3 

II. The Intermediate Course . - 19 



PART II. 

THE MATERIALS CONSTITUTING THE ASPHALT SURFACE 

MIXTURE. 

III. The Mineral Aggregate 29 

IV. Filler, or Dust k . . . 87 

V. The Nature op the Hydrocarbons which Constitute the 

Native Bitumens 97 

VI. Characterization and Classification of the Native 

Bitumens 110 



PART III. 
NATIVE BITUMENS IN USE IN THE PAVING INDUSTRY. 

VII. Differentiation and Characterization of the Native 

Bitumens 115 

VIII. Petroleums 127 

IX. The Solid Bitumens 147 

vii 



Vill TABLE OF CONTENTS. 

CHAPTER PAGE 

X. Individual Asphalts 156 

XI. Solid Native Bitumens which are not Asphalt 208 

XII. Asphaltic Sands and Limestones 221 

XIII. Residual Pitches, or Solid Bitumens Derived from As- 

phaltic and Other Petroleums 256 

XIV. Comparison of Various Native Asphalts and Their Rela- 

tive Merits for Paving Purposes 278 



PART IV. 

TECHNOLOGY OF THE PAVING INDUSTRY. 

XV. Refining of Solid Bitumens 291 

XVI. Surface Mixtures 313 

XVII. Asphaltic or Bituminous Concrete 375 

XVIII. Asphalt Blocks 389 

XIX. The Process of Combining the Constituents into a Sur- 
face Mixture 395 



PART V. 

HANDLING OF BINDER AND SURFACE MIXTURE ON THE 

STREET. 

XX. The Street 412 



PART VI. 
THE PHYSICAL PROPERTIES OF ASPHALT SURFACES. 

XXI. Radiation, Expansion, Contraction, and Resistance to 

Impact 425 

PART VII. 
SPECIFICATIONS FOR AND MERITS OF ASPHALT PAVEMENT. 

XXII. Specifications 435 

XXIII. The Merits of the Modern Sheet-asphalt Pavement . , . . 455 

XXIV. Action of Water on Asphalt Pavements 460 



TABLE OF CONTENTS. IX 



PART VIII. 

CAUSES OF THE DEFECTS IN AND THE DETERIORATION OF 
ASPHALT SURFACES. 

CHAPTER ._ PAGE 

XXV. Defects in and Deterioration of Asphalt Pavements . . 471 
XXVI. Maintenance of Asphalt Pavements 504 



PART IX. 

CONTROL OF WORK. 

XXVII. Instructions for Collecting and Forwarding to the 
Laboratory Samples of Materials in Use in Con- 
structing Asphalt Pavements 509 

XXVIII. Methods Exployed in the Asphalt-paving Industry for 
the Chemical and Physical Examination of the 

Materials or Construction 519 

XXIX. Solvents 589 

XXX. Equipment of a Laboratory for Control of Asphalt 

Work 595 

Appendix 599 



THE MODEM ASPHALT PAVEMENT. 



INTRODUCTION. 

The object of this work is to demonstrate the nature of asphalt 
pavements and the causes of defects in them, to bring about im- 
provement in the methods of their construction, and to show how 
this can be done. 

During an extended experience in the asphalt paving industry, 
which has included the inspection of the construction of asphalt 
pavements on behalf of a large city and the technical supervision 
of the work of several prominent companies which contract to 
lay them, it has been forced upon the attention of the writer that 
engineers, and others who are interested in obtaining the best 
results, have not been made sufficiently acquainted with the 
technology of the industry and with the importance of some of 
the engineering details involved to enable them to differentiate, 
at the time that the pavement is being laid, or even on its com- 
pletion, between good, bad, or medium work. Cities have, con- 
sequently, been obliged to rely on the statements and good faith 
of contractors, with the result that many asphalt pavements have 
eventually proved unsatisfactory, although when completed they 
were, to all outward appearance, of good quality — a condition which 
might have been readily avoided either by an intelligent super- 
vision of the materials in use and the manner of handling them, 
or by a change in the form of construction. 

It is proposed, therefore, to describe in the following pages 
the forms of construction which have been shown by experience 



2 THE MODERN ASPHALT PAVEMENT, 

to be the most satisfactory, the character of the materials enter- 
ing into the composition of asphalt pavements, the most refined 
methods used in the industry at the present day and the reasons 
which have led to their adoption, in order that engineers and 
others who are responsible for the supervision and character of 
such work may be able to distinguish between that of good and 
that of inferior quality. To this will be added specifications for 
asphalt pavements to meet various environments and use, and 
something as to their maintenance and the causes of their deterio- 
ration. 

The conclusions which are advanced are the results of twenty 
years' experience in the industry by the writer with pavements in 
over one hundred cities in the United States and in several in 
England, Scotland, and France, involving the construction of 
between twenty and thirty million yards of surface. 



PART I. 

THE FOUNDATION AND INTERMEDIATE COURSE, 



CHAPTER I. 
THE FOUNDATION OR BASE. 

The modern asphalt pavement in its perfected state is the 
evolution of thirty years of experiment and experience. It seems 
unnecessary here to give a history of the origin of this form of 
pavement on the Continent of Europe, or of the earliest experi- 
ments in the United States by De Smedt with artificial mixtures 
of sand and asphalt, as this information is readily available in numer- 
ous publications. It is sufficient to take the subject up at as late 
a date as 1894, when the first successful effort was made to place 
the industry on a rational basis as distinguished from the rule-of- 
thumb methods previously in vogue, and to follow it down to the 
most recent practice. 

An asphalt pavement consists essentially of a foundation or 
support for the surface which is to carry the traffic, itself supported 
by the soil, and a surface consisting of a mineral aggregate cement- 
ed together with asphalt to protect the base from wear and disinte- 
gration, between which is commonly interposed either a course of 
broken stone coated with bitumen, known as binder, or some sub- 
stitute for it, such as a cushion or separate course of the surface 
material, or a paint coat of bitumen dissolved in naphtha. These 
three elements of the pavement will be considered in turn. 

3 



4 THE MODERN ASPHALT PAVEMENT. 

The Subsoil Base. — As the foundation of a pavement, of any 
kind, is placed upon the soil and supported by the latter, it is a 
matter of vital importance that this latter support should be 
adequate, and it will only prove adequate if the subsoil is not 
subject to displacement from settlement or frost and is thoroughly 
drained. 

With sandy soils which are well compacted and which, from 
their nature, are well drained and dry there is no difficulty in the 
preparation of a satisfactory subgrade. Trenches in such soils, if 
they occur, can be solidly refilled with the aid of water. If the 
subgrade is a true sand, as in the neighborhood of seabeaches, it 
may be necessary, in order to compact the surface, to spread a 
course of gravel between the sand and the base in order to be able 
to roll it properly. 

With clay or heavy soils it is much more difficult to prepare 
a satisfactory subgrade, especially if this is likely to be subjected 
to the action of frost and if the original soil has been much dis- 
turbed by trenches, or if fills occur. If the subgrade consists 
of the original soil in situ, the only consideration necessary is its 
proper drainage, unless there are soft spots due to local causes, 
in which case they must be excavated and removed, with the sub- 
stitution of firm for the softer material. The satisfactory back 
filling of trenches in a heavy soil is a difficult matter. The use 
of water is a disadvantage in such work. Heavy soils absorb 
and hold it tenaciously and thus prevent thorough compaction, 
final settlement only taking place after the completion of the 
pavement. Trenches in such a soil should be carefully and slowly 
tamped in thin layers. 

The proper drainage of heavy clay soils is an essential feature 
in the construction of a satisfactory pavement, especially where 
these soils are apt to be thrown or cracked by frost in very cold 
climates, a condition which may be illustrated by that occurring 
in Manitoba, where cracks frequently open in the ground in 
winter, from four to six inches wide, and which would cause cor- 
responding cracks in the asphalt surface were not some provision 
made against it. For this purpose a form of construction has 
been evolved which has proved quite successful by providing sat- 
isfactory drainage and not laying the hydraulic concrete foundation 



THE FOUNDATION. 5 

in direct contact with the subsoil. Upon the subsoil clean sand 
and gravel are spread and rolled to a depth of three inches, 
and upon this the hydraulic concrete foundation is laid. At the 
same time, at intervals of twenty-five feet, trenches are cut 
in the subsoil to a depth of six inches, and filled with coarse 
broken stone; these cross-drains being connected with similar 
trenches, containing coarse broken stone, under the curb, which 
are graded to catch-basins for the removal of water. In such a 
climate tile drains cannot be used successfully, the author is 
informed by the City Engineer of Winnipeg, because the ground 
is generally frozen when the surface-water first begins to drain 
away and this water filling the tile often freezes and bursts it. 
The provisions in use in Winnipeg seem to be an ideal way of 
treating heavy soils in cold climates and, although absolutely 
necessary in such a location, are extremely desirable where any 
soil of such a description is found. Further details in regard 
to this method will appear in the chapter on " Specifications. " 1 

When a street is terraced and the roadway is lower than the 
adjacent property the greatest precaution should be taken to 
prevent the seepage from higher levels from working down between 
the soil and the foundation, or between the foundation and surface. 
For this purpose drainage should be provided below or along the 
curb, and at times in the subsoil itself. 

The most serious subgrade to encounter as a support for a 
foundation is marshy or swampy land, fills made on the latter for 
the purpose of raising the grade, or even fills on ordinary soils where 
sufficient time has not elapsed to bring about final settlement and 
ultimate compaction. Where such conditions are unavoidable 
good practice calls for the use of a sufficiently strong hydraulic 
concrete foundation to bridge over irregular settlement and to 
distribute the load over weak points. 

The cause of much of the deterioration in asphalt surfaces 
and in otner pavements is due to a neglect of such precautions 
in regulating the subgrade or in providing a foundation of a 
character to bridge over defects in the latter. 

1 Page 435. 



6 THE MODERN ASPHALT PAVEMENT. 

It seems hardly necessary to state that any subsoil should be 
thoroughly compacted by a heavy roller of broad tread, and that 
any weak portions revealed by the use of such roller should be 
removed by treatment in an appropriate way. 

The Foundation. — Foundations of most varied character have 
been used in the construction of pavements, including broken stone 
with or without a coating of more or less bitumen or coal-tar, mac- 
adam, old cobblestone pavement, an old surface of granite blocks 
or blocks turned and reset, old brick or asphalt-block surfaces, and 
hydraulic concretes of natural or Portland cement of varying thick- 
ness. Each of these forms has been more or less successful under 
different conditions, consideration being given to economy, to 
local environment, and to the traffic to be carried. 

Bituminous Foundation. — The so-called bituminous founda- 
tion possesses no advantage save, in some cases, that of economy. 
It has been almost entirely abandoned as a support for asphalt 
surfaces. It is a relic of the days when hydraulic cement was a 
much more expensive article than at the present time. As 
generally constructed it consists of six or more inches of broken 
stone passing a two or two and one-half-inch ring and not 
containing any particles passing a one or one and one-half-inch 
ring. Stone of such uniform size contains a large volume of 
voids, forty per cent or over, and does not compact well. Were 
it the run of the crusher, the foundation would be far more satis- 
factory. Under the roller much of the stone is often lost in the 
subsoil before the required thickness is attained. The coating of 
bitumen applied to the surface of the foundation is of little or no 
advantage. Enough cannot be used to fill the voids, as if this is 
done the excess will be drawn up into the surface by a hot sun 
and destroy or soften the latter while the cost would also be 
prohibitive. 

Additional disadvantages of such a foundation are that it pos- 
sesses no rigidity or stability and consequently responds at once to 
any settlement or weakness of the subsoil; that it is porous and 
allows the free movement of water and gas, and that the binder and 
surface cannot be readily removed from it for renewal without 
its destruction. 



THE FOUNDATION. 7 

Excellent asphalt pavements have been constructed with a 
bituminous foundation where the subsoil was firm and resistant 
and the travel light, as is the case in many residence streets, but 
surfaces equally good have been laid with broken stone alone. 
The cost of renewal of the surface of such pavements is, however, 
high, as has already been shown. 

Macadam Foundation. — Old macadam has been used success- 
fully in several instances as a foundation for asphalt pavement. It 
possesses many advantages over broken-stone. In macadam the 
voids in the stone are well filled with finer particles and it has 
received its ultimate compression under travel. It has not a 
coating of bitumen, so that the binder and surface coats are readily 
removed for renewal. It possesses the defect that the grade of 
the macadam can be altered but slightly without serious disturb- 
ance of its bond, and in replacing the pavement over trenches the 
stone becomes far less of a support than the original macadam. 
It, of course, presents the merit of economy. An excellent example 
of an asphalt pavement with a foundation of this class is to be seen 
on Broadway, above Fifty-ninth Street, in New York City, and on 
Michigan Avenue, to the south of Congress Street, in Chicago, 
111. The former street has been trenched to a large extent, and 
repairs have resulted very satisfactorily. The latter has a few 
cracks owing to the action of frost. 

Other Old Pavement as Foundation.— Old cobblestone and 
asphalt-block pavements form an excellent foundation for asphalt 
pavements if the height of curb shown is sufficient and the amount 
of traffic permits. They should not be used if resetting is necessary 
except on very favorable soil and with the expectation of very 
moderate use. 

Old granite-block pavements have been very extensively used 
for supporting asphalt surfaces, especially in New York City, 
and their value for this purpose and the defects which result there* 
from are well illustrated there. Granite blocks laid in sand on 
the soil have been found very satisfactory on cross-town residence 
streets, but have been most unsatisfactory on streets like First 
Avenue, where the subsoil is soft, fills are frequent, and partly on 
land below high-water mark, in bringing the street originally to 



S THE MODERN ASPHALT PAVEMENT. 

grade. These blocks could be seen to move under the steam-roller 
when the binder course was laid, and the asphalt surface is, in con- 
sequence, in constant need of repairs. The only foundation which 
would prove satisfactory under these conditions would be, con- 
sidering the heavy travel on the street, the best form of Portland- 
cement concrete to a depth of at least eight inches. 

Granite blocks on concrete make an excellent foundation for 
an asphalt surface, if not reset, but where the grade necessitates 
taking them up and replacing them on their broad sides the result 
is not satisfactory except on residence streets. When relaid they 
are not rigid, but have a tendency to rock under heavy travel. 
Such a foundation supports the asphalt surface on Broadway and 
several avenues in New York City, and has not been entirely 
successful. The turned blocks were opened to travel for some time 
to bed them thoroughly, and any loose ones reset. The binder 
and surface were then laid directly on the blocks. The vibration 
on these blocks, especially along the rail, is nevertheless large. 
A better form of construction would be to grout the blocks, after 
turning, with Portland cement, and keep traffic off of them until 
the grout is set. The lesson is that turned granite blocks should 
not be used as a foundation for asphalt pavements on streets of 
heavy travel, even when supported by Portland-cement concrete, 
and much less so on soil alone, as has recently been done on 
Fourth Avenue in New York City. 

Construction of this description inevitably results in deteriora- 
tion of the best asphalt surfaces, with the results that the defects 
are attributed to the asphalt and not to the foundation where they 
really originate. As a matter of fact no foundation is suitable for 
a street of heavy travel except one of Portland-cement concrete 
of sufficient depth and strength to carry the load imposed upon the 
surface with perfect rigidity, and it is equally true, as determined 
by years of careful observation, that ninety per cent of the defects 
in asphalt pavements in such cities as New York, where the sur- 
face mixture is of standard quality, are due to the insufficiency 
of the foundation. 

Old brick pavements have served as a support for asphalt sur- 
faces with entire satisfaction. They have received the full traffic 
of the street to be resurfaced and are therefore well compacted. 



THE FOUNDATION. 9 

Such pavements, as their surfaces become too uneven for use, will, 
in the future, be largely renewed in this way. 

Hydraulic- Concrete Foundation. — Hydraulic concrete, if prop- 
erly proportioned, made with good cement and a well-graded 
aggregate, well mixed and put in place satisfactorily and in good 
weather, is the ideal foundation. Unfortunately these conditions 
are not always met. To discuss the possible variations and de- 
ficiencies in detail would be to write an elaborate treatise on the 
subject of concrete. It will suffice, however, to point out the chief 
merits and defects which appear most strongly in its use as a 
foundation for pavements. 

The proportions of the different constituents, from which the 
contractor cannot depart, are sometimes injudiciously prescribed, 
and usually from motives of economy. In an eastern city a 
concrete foundation is specified which is to consist of one (1) part 
of Portland cement, four (4) parts of sand, five (5) p # arts of gravel, 
and five (5) parts of stone. While such a foundation may have 
sufficient strength to support a pavement carrying moderate travel, 
it is nevertheless porous and permits of the free movement of water 
and gas from below, both of which act on asphalt under such 
circumstances. The most favorable proportions which the writer 
has observed for a concrete for heavily travelled streets are those 
which were prescribed for Fifth Avenue, in New York City, in 1896. 
These were; one (1) part of Portland cement, three (3) parts of 
sand, two (2) or three (3) parts of gravel, and four (4) or five (5) 
parts of broken stone. If the stone were large the larger amount 
of gravel was used and the reverse. The gravel in the preceding 
concrete is of the greatest aid in filling the voids in the stone and 
in facilitating the compaction of the concrete when rammed. Stone 
with sand alone is very apt to bind, bridge, and resist compaction, 
while the voids are so large as to leave at times a portion of them 
unfilled with mortar. 

The foundation thus constructed on Fifth Avenue has a depth 
of at least seven inches and is absolutely rigid. The asphalt sur- 
face placed on this is subject to no vibration and has shown no 
deterioration due to this cause in twelve years, while the same 
surface mixture supported only by the granite blocks on a soft 
soil in First Avenue was in far from good condition in a year. 



10 THE MODERN ASPHALT PAVEMENT. 

This contrast between the two avenues with their different founda* 
tions is, therefore, most instructive and points to the fact that the 
primary consideration in an asphalt pavement is the foundation 
which supports it. Without a rigid one the best of materials and 
workmanship in the remainder of the pavement will go for naught. 

Ordinary practice as regards the aggregate in a hydraulic 
concrete provides for broken stone all of which "will pass in any 
direction through a revolving circular screen having holes two and 
one-half (2J) inches in diameter and be retained by a screen hav- 
ing holes one (1) inch in diameter." * This may be good prac- 
tice, but is certainly not the best. 

The grading of the broken stone is an important consideration 
in adjusting the relations of the constituents in a well-proportioned 
concrete not only in a foundation for asphalt pavements, but in its use 
for every purpose. Fortunately this is rapidly becoming recognized. 
As has already been mentioned, the voids in broken stone passing 
a two-inch ring and not passing an inch and one-half or a 
one-inch ring are very large in volume, and it has been, and 
generally is, the practice to attempt to fill them with a mortar of 
one part of cement and three parts of sand, in the case of 
Portland, or two in the case of natural cement. This is not 
economical in more ways than one. It is much better to reduce 
the voids by using the broken stone as it comes from the crusher 
in well-assorted sizes and with smaller voids, the screenings passing 
a quarter- or three-eighth-inch screen only being removed, on 
account of its tendency to segregate and because it should actually 
be considered as sand, as will appear later, or to add gravel where 
it is available or where economy demands the separation of the 
inch stone for use in binder. The mortar then goes much farther, 
is not in such large masses, and the concrete is rammed and com- 
pacts with much greater ease. Under such circumstances, while 
the proportion of cement and sand should not be extended beyond 
one of the former to three of the latter, corresponding to the 
relation of the volume of the cement to the voids in the average 
concrete sand, the proportion of stone to the mortar may be largely 

1 Manhattan (New York) Specifications, 1901, paragraph 12. 



THE FOUNDATION. 11 

extended beyond that which may be safely allowed for stone of 
uniform size and large voids. 

Where good gravel is available, containing particles of suf- 
ficiently large size, a concrete made with this material without the 
use of crushed stone may be as equally satisfactory or even preferable 
to one constructed with stone alone or with a mixture of stone and 
gravel. A provision for such concrete is now contained in the speci- 
fications of some of our cities. 

Where gravel occurs mixed with the requisite proportion of 
sand such a natural mineral aggregate can be employed in the 
manner in which Thames ballast is used in London, England, and 
with the most satisfactory results. The occurrence of such deposits 
in the United States is exceptional. 

Another fortunate thing in recent practice is the recognition 
of the facts that a concrete the mortar in which is wet enough to 
almost quake under the tamper gives the most satisfactory results, 
since the slight early loss in strength due to the water excess is 
more than made up by the improved and thorough compaction 
attained. Dry concrete is no longer regarded as good prac- 
tice. 

In the early days of the asphalt-paving industry hydraulic 
concrete was usually mixed by hand labor on boards. To-day 
much of this work is very satisfactorily and much more cheaply 
done with the use of mixers driven by power. Of these there are 
a number of successful types now on the market, and, from the 
author's observation, they are strongly to be recommended where 
the extent of the work will justify their being employed. 

Concrete Sand. — It is usually specified that sand in use in 
concrete sha'l be clean, coarse, sharp, and free from loam and dirt. 
The degree of coarseness is generally somewhat indefinitely expressed. 
Concrete sand as a rule contains but a small percentage of grains 
finer than will pass a fifty-mesh sieve. It may, however, con- 
tain to advantage a considerable portion of fine gravel. In this 
connection it may be remarked, however, that the permeability 
of a concrete is greater the coarser the sand, and that the presence 
of some fine grains is not undesirable. A small amount of loam 
or clay in sand is not injurious if it is not present in a lumpy con- 



12 THE MODERN ASPHALT PAVEMENT. 

dition. Many pit sands which have been rejected on account of 
the presence of loam make excellent concrete. 

Crusher Screenings.— Sand has been defined as the detritus 
of rock, smaller than gravel and larger than silt. Under such a 
definition the screenings from the crushing of rock for the pro- 
duction of broken stone is sand and may be used as such in concrete. 
Its use for such purposes has attracted very considerable attention 
recently, and the results obtained with it have been most successful. 
The strength of the concrete in which sand is replaced by screenings 
is always equal to and in many cases in excess of that made with 
natural sand. It has been used, and pronounced a desirable 
material, in the concrete of the Buffalo breakwater, 1 in the Man- 
chester and Liverpool (England) water-works, 2 in the Jerome 
Park Reservoir in New York City, in masonry construction on the 
C. M. & St. P. R. R., and in the concrete on the Water-power 
Sections Nos. I, 2, and 3 of the Chicago Drainage Canal. It has 
been tested by many engineers in the laboratory and found to 
produce concrete exceeding or equalling in strength that made with 
sand. An excellent resume of the availability of this material 
will be found in "The Cement Age," Vol. 1, No. 3, page 5, August 
1904, and in a publication of the Producers' Supply Company, 
entitled " Crushed Stone and its Uses/' pages 100, 103, and 107, 
Chicago, 1904. 

It has been successfully used in the concrete foundation for asphalt 
pavements in several cities, and its use for this and other purposes 
is rapidly increasing. The author made the following statement 
in connection with the use of crusher screenings as a witness before 
the Aqueduct Commissioners of the City of New York when this 
was objected to by the Merchants' Association of the city: 

"The advantages are that the particles in the crusher screen- 
ings are better graded in size, and in consequence those screenings 
have a smaller volume of voids or unfilled cavities in them. As 
a result a definite volume of Portland cement will go farther 
towards filling those voids than with sand, where the particles 



1 Eng. News, Sept. 11, 1902. 

2 Hill, Institution of Civil Engineers, London, 1896; Deacon, ibid. 



THE FOUNDATION. 13 

are more uniform in size and the volume of the voids large. . . . " 
There can be no question that crusher screenings are preferable 
to many natural sands when the rock in which they originate is 
of desirable quality. 

Character of the Hydraulic Cement in Use. — The character of 
the hydraulic cement in use in concrete foundations is as important 
as any constituent of the pavement. If it is defective in any way, 
the result will be shown in the surface. In one case one of the 
most prominent surfaces in the country became cracked across 
the street at wide intervals two years after it was laid, and in three 
years the surface was noticeably raised at these points. On open- 
ing the pavement the cracks in the surface were found to be due 
to cracks in the concrete formed during the first two years, and 
the elevation of the surface, which occurred later, to the subse- 
quent expansion of the cement, which in this way pushed one 
portion of the foundation upward and over the other, although the 
cement was a Portland and one which responded satisfactorily to 
all short-time tests for constancy of volume. A similar exper- 
ience was met with for several years with the natural cements of 
western New York, and it was generally necessary, where one 
brand was used, to remove the surface and cut out the expanded 
portion after a few years in order to bring the surface of the 
pavement to grade. 

In the middle West serious troubles due to the character of 
the natural cement in use were often met with befoie Portland 
cement became available. The natural cements of that part of the 
country are not always reliable or uniform and are especially un- 
suited for use in cold weather, as they fail to set when the tem- 
perature approaches freezing. The writer has frequently seen 
hydraulic foundations which have acquired no bond, either from 
their inferior quality alone or because of use in cold weather. Such 
a foundation is open and porous and allows water to reach and 
disintegrate the asphalt surface. It frequently cracks after a firm 
set has taken place, and these cracks are eventually repeated in the 
asphalt surface, as can be seen in the accompanying illustration, 
Fig. 1 . The evident conclusion is that the use of natural cement 
in concrete for the foundation of asphalt pavements should be 




Fig. 1. 



14 



THE FOUNDATION 15 

abandoned, although it would not be justifiable to suppose that 
none made from this cement or even the majority of it is poor. 
That under the first asphalt pavement of any area, on Pennsyl- 
vania Avenue, Washington, D. C, was constructed with natural 
cement from the Potomac Valley, and during thirty years gave 
entire satisfaction. Foundations containing the Rosendale cem- 
ents have proved equally good, but all the natural cements of 
this description attain their strength so slowly that an unfortu- 
nately long period must elapse before they will safely sustain a heavy 
roller suitable for compressing the binder and surface, and in this 
way the completion of. the pavement is delayed. It is therefore 
much better to avoid using natural cements, and the substitution 
of Portland cement has become the very general practice. 

All hydraulic cement in use in the construction of asphalt 
pavements should be tested before it is allowed to go into the 
work, and should meet the requirements which the local engineer 
believes to be reasonable. The Committee on Uniform Tests of 
Cement of the American Society of Civil Engineers has recom- 
mended methods which should bring about greater uniformity 
in testing cements, and their use is suggested. 1 

A similar committee of the American Society for Testing Mate- 
rials has recommended reasonable specifications for cement which 
can be adopted if they meet with the approval of the engineer. 2 

Lateral Support. — Closely related in importance to the char- 
acter of the foundation of the pavement is that of the lateral sup- 
port which the surface receives. 

It is quite as well proved by experience that more defects 
in asphalt surfaces are due, proportionally to the area involved, 
to the lack of this than to weak foundation and, often, to all other 
causes. 

The lateral support should be as rigid as in the case of the 
foundation, and unfortunately it is not always so about manholes, 
water- and gas-boxes, at headers where the surface ends, and espe- 
cially against rails. Vibration about manholes, boxes, etc., can be 

1 Proceedings Am. Soc. C. E., 1903, 29, No. 1. 

2 Report of Committee C on Standard Specifications for Cement. Pre- 
sented at Annual Meeting, 1904, June 17. 



16 THE MODERN ASPHALT PAVEMENT. 

avoided by providing heavy castings with a broad base and set- 
ting them upon a proper foundation in Portland cement a suffi- 
ciently long period before laying the surface to prevent them from 
being loosened by a blow from the roller. Headers should be 
sufficiently heavy to hold the surface up and resist the impact 
of traffic. 

The construction of a street car-track the rails and sleepers 
of which shall be sufficiently free from vibration to form a sup- 
port for an immediately adjacent asphalt surface is a most diffi- 
cult matter and one that is rarely successfully carried out, espe- 
cially when trolley-cars of the size and weight of those in use 
to-day are to be considered. 

Experience has shown that construction involving the use of 
a very heavy girder-rail placed upon ties, which, together with 
the rail, are embedded in concrete from the base of the former 
to the height of the adjoining foundation of the pavement, is the best. 
Such construction will be, however, of little value if traffic is 
allowed over the rail before the concrete has had time to set thor- 
oughly. In cases where the soil is very heavy and the drainage 
is bad crushed stone used as ballast may often prove more satis- 
factory than hydraulic concrete, as affording better drainage. 
Where mud forms, owing to poor drainage, and works into cracks 
between the asphalt surface and the concrete the result is very 
disastrous. 

Another form of rail construction which has met with con- 
siderable approval is the placing of the rail upon a hydraulic con- 
crete beam extending its entire length. It is possible that this 
may be desirable where carefully carried out, but, in the author's 
experience, where a girder-rail of sufficiently heavy type is to be 
used no advantage is derived commensurate with the expense, and 
the possibility of vibration is not lessened. 

If vibration still takes place in a rail, even with the best form 
of construction, and this is rarely absent with heavy trolley-cars, 
a triple row of the best paving-blocks, or bricks, laid with broken 
joints parallel to the rail should be placed against it, bedded in 
cement, and well grouted, depressing the base sufficiently for 
this purpose. Header and stretcher construction is most faulty. 
The asphalt toothing is then a point of weakness. 



THE FOUNDATION. 17 

Vibration of the rail will eventually destroy an immediately 
adjoining surface not only by breaking the bond between the 
particles of the surface, but by admitting water and mud after 
the first fracture has taken place. 

All the defects which are due to weakness in the foundation and to 
the lack of lateral support involve not only an expense to the 
contractor during the guarantee period which he must consider 
in his bids after a study of the form of construction specified by 
the city, but will also prove an additional cost to the city when 
it takes over the maintenance of the street. Economy in the cost 
of the pavement in this direction may not prove true economy 
in the end. 

While it is not, of course, necessary that a needlessly expen- 
sive foundation should be provided for an asphalt pavement, it will 
eventually prove cheaper if a good margin of safety in this direc- 
tion is allowed. An asphalt surface is no stronger than its weak- 
est part. 

SUMMARY. 

It appears that better concrete can be made of graded 
broken stone than of stone of uniform size, that the addi- 
tion of gravel is an improvement, that a concrete consisting of 
gravel alone as a substitute for broken stone will often prove sat- 
isfactory, that crusher screenings are an excellent substitute for 
natural sand, that Portland cement is infinitely preferable to 
natural cement, that the greatest care should be used that the 
pavement should have a proper lateral as well as vertical support, 
and that the greatest attention should be paid to the rigidity of 
railroad-track construction. 

It seems, therefore, that while an asphalt pavement of the 
best quality can be constructed only when all its elements — foun- 
dation, binder or its substitute, and surface — are of the highest degree 
of perfection, refinement in the character of the binder and sur- 
face is thrown away if the subsoil is not satisfactorily drained and 
if the foundation of the pavement is not sufficiently strong to carry 
the traffic to which the surface is subjected with entire rigidity 



18 THE MODERN ASPHALT PAVEMENT. 

and is not sufficiently impervious to protect the surface from the 
action of water and illuminating-gas. 

In addition a well-constructed foundation is a matter of 
economy, as it should last for all time and will only require 
resurfacing at intervals, whereas an inferior one must eventually 
be renewed by one properly constructed. 



CHAPTER II. 
THE INTERMEDIATE COURSE. 

In the early days of the asphalt-paving industry a thicker 
wearing surface was in use than to-day. That of 1876 on Pennsyl- 
vania Avenue in Washington, D. C, and most of those laid in the 
following fifteen years were two and one-half inches thick. These 
surfaces were laid in two courses, and are thus described in an 
old specification of a Washington contractor in 1878: * 

"The asphalt (surface mixture), having been prepared in the 
manner thus indicated, is laid on the foundation in two coats. 

"The first coat of one-half inch thickness, called protecting 
coat, might be laid richer in asphaltic cement, and may be consoli- 
dated simply by rolling with iron or stone rollers weighing about 
1000 pounds or half a ton. 

"On this first asphalt coat is then carefully spread with iron 
rakes the final finishing coat," etc., etc. 

It is evident from this that the one-half-inch coat of surface 
mixture was laid for no other purpose, at this time, than to pro- 
tect the rather friable hydraulic concrete of natural cement from being 
broken up by hauling the final surface mixture over it. It will 
be noted that it is suggested to lay the first coat of material richer 
in asphalt cement. 

In 1884 the specifications which the city itself adopted were 
evidently based on those of 1878, but the wording was somewhat 
changed, "pavement mixture" replacing "asphalt" in the first 
paragraph quoted, and "cushion coat" for "protective coat," with 
some other minor alterations, in the second, the thickness of the 

1 Rept. of Com. D. C, 1878, 292. 

19 



20 THE MODERN ASPHALT PAVEMENT. 

latter remaining one-half inch " after being consolidated by a 
roller/' while it is to contain, specifically, "from two to four per 
cent more asphaltic cement" than the "surface coat." 

In the interval mentioned the term "protective coat" which 
casts some reflection on the character of the foundation has, therefore, 
been changed to "cushion coat." The greater richness of the cush- 
ion has been retained. 

In the specifications for 1886-87 no mention is made of a pro- 
tective or cushion coat. It is provided that the surface mixture 
will be "carefully spread, in such a manner as to give a uniform 
and regular surface and to such depth as, after having received 
its ultimate compression of 40 per cent, to have a thickness of 2 J 
inches." 

The cushion coat was temporarily abandoned in that year. The 
reason for this is instructive, as showing the defects of this method 
of construction. Surfaces laid with a thickness of two and one- 
half inches the lower part of which consisted of a protective 
or cushion coat richer in bitumen were liable to serious displace- 
ment under travel, with the result that the surface became very 
wavy and uncomfortable to drive over, an experience met with in 
other cities as well, and which subjected such asphalt pavements 
to unfavorable comment. The excessive thickness and the richer 
cushion coat permitted not only of this displacement of the sur- 
face, but also allowed its movement on the foundation under 
the impact of wheels of vehicles, when once the waves were formed, 
especially where travel, as in streets with car-tracks, was confined 
in one direction. 

The change in the specifications in 1886-87 was intended to 
avoid this by doing away with the cushion and compacting the 
entire surface at once. It was an improvement, but for some reason 
the provision for a cushion coat one or two per cent richer in asphalt 
appeared again in the specifications for 1887-88. No asphalt 
pavements were laid in Washington during this fiscal year, as the 
city was compelled, by provisions in the act making appropriations 
for the purpose, not to go beyond a limit in price for such pavement 
for which the contractors refused to lay asphalt. A return was, 
therefore, made to coal-tar with disastrous results, the only gain 



THE INTERMEDIATE COURSE. 21 

being that when asphalt surfaces were again laid in 1888 the ex- 
cessive thickness of the surface was reduced and a course of broken 
stone coated with coal-tar or asphalt was introduced which had 
been an element of the so-called distillate pavements of the inter- 
mediate period. This gain was a distinct one for the asphalt- 
paving industry all over the country, as it did away with the dis- 
placement of the thicker surface under traffic. No general return 
to the original method of construction without this course has been 
made since that time except in two or three cities, and there with 
less unsatisfactory results than formerly owing to the more careful 
grading of the mineral aggregate in modern mixtures and their 
greater stability. 

The Binder Course. — The binder course, as has been said, is 
an inheritance from the days of coal-tar pavements with broken 
stone foundations, and its use in combination with an asphalt sur- 
face was the result of an attempt to improve upon the unsatis- 
factory distillate pavement, so called, laid in Washington in 1887, 
by substituting an asphalt for a coal-tar surface, leaving the 
foundation and binder unchanged. Eventually a hydraulic con- 
crete foundation was substituted for the broken stone and the re- 
sult was the modern form of construction. 

The binder course was evidently the result of an attempt to 
close the large openings in the broken-stone foundation by a course 
of finer stone in order to prevent the loss of the more expensive 
surface mixture by its compression into the voids of the former 
and with no idea of preventing displacement in the surface. That 
it accomplished this was only detected when it was noticed that 
its use as a matter of economy in reducing the thickness of the 
asphalt surface from two and one-half to one and one-half inches 
produced this desired result. From Washington in 1888-89 the 
binder course rapidly spread over the country and proved suc- 
cessful. In its original form it consisted of "clean broken stone, 
thoroughly screened, not exceeding one and one-fourth (1 J) inches 
in the largest dimension and No. 4 coal-tar paving cement." 

The coal-tar was soon replaced by an asphaltic cement and 
the broken stone in some cities by a smaller stone passing an inch 
ring with the grit and finer material removed. 

From a binder constructed in this way there has been little 



22 THE MODERN ASPHALT PAVEMENT. 

departure for many years, although recently the possibility of 
some improvement in this course has become very evident. The 
original course was one and one-half inches thick when compacted, 
a depth quite necessary with one and one-fourth inch stone. With 
finer stone and for economy inch binder has frequently been speci- 
fied, but there can be little or no bond to such a thickness and 
its use in this way is plainly poor practice. 

It is generally specified that the binder stone shall pass a one 
and one-fourth- or one-inch screen and contain not more than 
a certain percentage of fine material. This is a great mistake, 
as in the case of hydraulic concrete, since the more fine material 
the stone contains, up to the point where the voids in the large 
particles are filled, the more compact and desirable the binder is. 
At the same time a binder with much fine material requires a 
larger amount of asphalt cement and is consequently more expen- 
sive. If the contractor is willing to assume this extra expense 
no objection can be raised to such a practice. 

The amount of asphalt cement necessary to coat satisfactorily 
a binder of clean stone, free from grit and dust will vary with the 
character of the stone and the nature of the asphalt cement. With 
Hudson River limestone or trap three per cent of bitumen is 
sufficient, and this is represented by that amount of an asphalt 
cement composed of pure bitumen or four per cent of one made 
with Trinidad asphalt. With the softer limestones of the middle 
West, a higher percentage is occasionally necessary. The exact 
amount can only be determined by experiment. It should not be 
sufficient to run off of the hot stone or too little to give a bright 
glossy coat. An excess may result disastrously, as it will collect 
inevitably in pools or spots where the binder has been taken from 
the bottom of the truck in which it has been hauled to the street, 
and the excess collecting at these points may be drawn up by a 
hot summer sun and soften the surface of the pavement or even 
appear in mass thereon, as has happened in one or two instances 
in a western city. 

On the other hand, a slight and well distributed excess may 
prove of decided benefit on streets having little or no traffic, where 
the surface would be apt to crack ordinarily. It has been found 



THE INTERMEDIATE COURSE. 



23 



that in such a case the surface is slowly enriched by the excess, 
and is thus preserved. 

An example of this enrichment was observed in an Alcatraz 
surface laid on a very rich binder in a western city in 1889. A 
specimen of the surface was analyzed several years after it was 
laid, after separating it into top and bottom sections. The results 
were as follows: 





Bitu- 
men. 


Passing Mesh. 




200 


100 


80 


50 


40 


30 


20 


10 


Top 

Duplicate. 

Bottom. . 
Duplicate. 


9.8 
9.8 

10.3 
10.7 


12.2 
11.2 

11.7 
11.3 


10 
10 

10 
10 


31 
31 

32 
33 


32 
33 

32 
31 


3 
3 

2 
2 


1 
1 

1 
1 


1 
1 

1 
1 










The bottom of the pavement carries, on an average, seven-tenths 
per cent more bitumen than the top, and that this is no accident 
in mixing appears from the uniformity of the sand grading in 
all the samples of the different sections. 

The consistency of the asphalt cement in use in binder should 
be softer than that in the surface for several reasons. The ordinary 
binder is a very open material which permits the volatilization of 
oil from the asphalt cement by the heat of the stone, especially 
if the stone is accidentally too hot and the haul to the work a 
long one, with the result that the cement becomes much hardened 
and more brittle. In the second place the tendency to the rupture 
of the bond between the fragments of binder stone is much less 
with an asphalt cement of soft than of hard consistency. 

Good practice leads to the use of a cement for binder which 
is twenty or more points softer, by the penetration machine, 
than that in the surface. 

The actual temperature of the binder as it is laid on the street 
should be no greater than is necessary to make it possible to rake 
it out. It may be much colder than an asphalt surface mixture. 

Recent experience has shown that there are defects in such 
a b'nder which are due to the fact that the voids are unfilled and 



24 



THE MODERN ASPHALT PAVEMENT. 



the course lacks stability and solidity. Such defects have been 
manifested in two ways for many years. If binder is not laid with 
great attention to the character of the asphalt cement which covers 
the stone and binds it together it soon loses its bond under heavy 
traffic and, the stone itself having but little supporting power, 
the asphalt surface goes to pieces. If, on the other hand, the 
binder stone itself is not a strong one it is frequently crushed by 
the weight of heavy traffic and the surface, losing its support, 
either goes to pieces or the crushed binder is forced into it irregu- 
larly, thus causing a decided displacement which eventually results 
in disintegration. 

In individual cases the surface has been observed to have been 
driven by traffic into the voids in the binder without displacement, 
with the result that the thickness of the pavement has been much 
reduced, although in this condition it is a much more rigid mass 
than as it was first constructed. 

The binder previously described has consisted of stone prac- 
tically or largely of one size, three-quarters to one and one-half 
inches in the largest diameter, as appears from the following an- 
alyses : 



Test number 

Bitumen 

Filler 

Sand 

Stone : 
Passing \" sieve 

" r " 

Retained 1" " 



69978 
5.4% 

2i:o} 26 - 8 



5.8 
13.6 
41.4 

7.0 



67.8 



100.0 



70804 



4.4% 
4.1 
12.5 



1C0.0 



16.C 



79.0 



70854 



3.8% 

2.2 

7.5 



1C0.0 



9.7 



86.5 



71102 

3.6% 

2.4\ 
3.0/ 



5.4 



13.5 
51.5 

26.0 
0.0 



91.0 



100.0 



74893 



100.0 



4.5 



92.0 



It will be seen from the preceding results that the percentage 
of bitumen which binder will carry depends largely upon the 
amount of fine materiel which it contains, binder No. 69978 with 
26.8 per cent of fine material holding 5.4 per cent of bitumen, while 
those made from cleaner stone where the fine material does not 
exceed 5 per cent, carry less than 4 per cent of bitumen. If the 



THE INTERMEDIATE COURSE. 25 

stone in use is not screened, but contains all the finer particles 
coming from the crusher, the binder will be more satisfactory. 

Asphaltic Concrete Binder. — The weakness of the ordinary 
open-binder course, where subjected to heavy traffic, can be 
avoided by filling the voids in the material with fine stone or grit 
and the remaining voids, after this addition,, with sand or a mineral 
aggregate corresponding in grading to that of a standard surface 
mixture. 

Such a binder has given most excellent results in supporting 
an asphalt surface on an ordinary foundation, such as turned or 
reset blocks or alongside of poorly constructed street-railway 
tracks, such as those on Broadway in New York City, being in 
itself perfectly rigid. 

A good example of this form of construction on a hydraulic 
concrete foundation may be seen on Court Street in Boston, from 
Washington Street to the old Court House, and on Kilby Street 
in the same city, between State and Central Streets. A photograph 
of a sawn section of such pavement is shown in Fig. 16. 

The manner in which a binder of this type, which 'is generally 
known in the industry as close or compact binder, .is turned out at 
the plant is much the same as that used in preparing an as- 
phaltic concrete to be 'used as a wearing surface, with tne exception 
that it contains no filler, and will be described in a later chap- 
ter. It will be of interest, however, to give some examples of the 
proportions in which the various components have been employed 
in actual practice during the year 1907, together with the results 
of analyses of the finished binder. (See Table on page 26.) 

Close binder of the Boston type is probably more desirable than 
that produced in New York, owing to the larger percentage of 
three-quarter inch stone which it contains and its consequent 
greater stability, but as the stone at that point is not separated 
into two sizes after heating, but drawn from one bin, there is 
probably a greater amount of segregation in the mixture than in 
that turned out at New York, where stone of each size is separated 
and weighed out in definite proportions. Nevertheless, a very 
satisfactory asphaltic concrete for the binder course has been 
turned out in Boston in that way, with the exception that where 



26 



THE MODERN ASPHALT PAVEMENT. 





New York. 


Boston. 




Plant 1. 


Plant 2. 




Coarse stone 


480 lbs. = 54. 6% 
200 " 22.7 
150 •• 17.0 

50 " 5.7 


480 lbs. = 53.3% 
202 " 22.4 
150 " 16.7 
68 " 7.6 


} 885 lbs. =73 4% 


I* ine stone 




250 " 20.8 


Trinidad asphalt cement 
Bermudez " " 


70 " 5.8 




880 lbs. 100.0 


900 lbs. 100.0 


1205 lbs. 100.0 



Analyses: 



Bitumen soluble in CS 2 . 


5.6% 


5.2% 


4.8% 


Passing 200 mesh screen 


4.4 


6.4 


4.2 


10 " 


29.2 


29.0 


26.4 


it 1 u u 

8 


1.8 


2.0 


.8 


" I inch " 


10.0 


7.0 


4.4 


i a 


23.2 


25.8 


24.4 


u 3 a <♦ 


13.6 


17.8 


32.2 


n tt ft 


7.4 


6.8 


2.8 


Retained 1 " 


4.8 


0.0 


0.0 




100.0 


100.0 


100.0 



there is segregation of the finer material, it sometimes happens 
that there will be a displacement of the surface of the finished 
pavement at that point. 

On this account, there are one or two points which experience 
has shown must be guarded against. The fine material should 
not be at all in excess of an amount sufficient to fill the voids in 
the stone, since, if this is the case, too smooth a surface will be 
obtained, with resulting displacement of the wearing surface. An 
excess of bitumen must also be avoided for the same reason. 

In the construction of an asphalt pavement with an asphaltic 
concrete binder course, the surface should be applied to the binder 
before it has become entirely cold, in order to obtain a satisfactory 
bond. It is not possible to do satisfactory work where a large area 
of close binder is laid on one day and covered with surface on the 
next. There should be an alternation of the binder and surface 
courses, for example, no more binder should be laid in the begin- 



THE INTERMEDIATE COURSE. 27 

ning of a day than can be covered with surface during the remain- 
der of the available working hours. 

Where old surface mixture is available and facilities are at 
hand for softening this by means of heat or by grinding it in a 
disintegrator, such material can be used quite as satisfactorily 
for filling the voids in an ordinary binder as new sand and filler, 
thus reducing very much the cost of a concrete binder course. 
The percentage of asphalt and its consistency in such a case will, 
of course, be regulated by the amount already present in the old 
material. 

The form of construction involving the use of a compact binder 
naturally increases the cost of the pavement to a certain extent, 
but the advantages gained more than make up for this, since its 
life will be extended to a degree more than sufficient to bring the 
cost per year below that of one in which the old open form of binder 
is used, especially on streets of heavy travel. In the author's 
opinion it is the most important advance that has been made in 
the asphalt paving industry since the evolution of the rationally 
graded surface mixture in 1896. Its use is specified in Kansas 
City and Omaha, as can be seen in the very excellent specifications 
of the former city, which are reprinted in the appendix. 

Paint-coat. — Some of the defects in a pavement due to an 
open binder can, perhaps, also be removed by abandoning it entirely 
and substituting therefor a so-called paint course which con- 
sists of an asphalt cement of suitable consistency dissolved in 
benzine, 62° B., and then applied with a brush or squeegee to the 
surface of the hydraulic foundation, which should be made, if this 
coat is used, of Portland cement, or else floated with a mortar of 
this cement, and should have a comparatively smooth surface. 
The coating should be bright and glossy, but not sticky, and it 
must be carefully protected from becoming dirty. It cannot 
be applied successfully to a concrete that is in the slightest degree 
damp, as the adhesion is then imperfect. If well done, and this 
requires some skill and experience, the surface mixture applied 
directly to this coat will be cemented firmly to it and any displace- 
ment in the surface on the foundation will be prevented if the 
mixture itself is stable . 



28 THE MODERN ASPHALT PAVEMENT. 

The first use of such a coat as a substitute for binder was made 
in a town in Ohio in 1896, where an asphalt surface was laid on 
an old brick pavement, the grade of which did not permit of the 
use of a binder course. The adhesion of the surface to the brick 
was afterwards found, on making cuts for water and gas connec- 
tions, to be so strong that the upper portions of the brick were 
torn away with the asphalt surface. On one or two streets in 
New York on which very heavy coal trucks are constantly passing, 
and where the binder course was frequently crushed, a similar 
construction on a Portland-cement base was successful. 

Specifications for the use of paint coat are as follows: 
"Upon the surface of the foundation of the Portland cement 
concrete, a paint course shall be applied to bind or tie the surface 
course to the foundation. For this purpose, the surface of the 
cement concrete shall, in its preparation, be well rammed, so that 
mortar shall come to the top, and it shall be made so smooth that 
no depression shall exist of a depth of more than three-eighths (■£) 
of an inch. The paint for use shall consist of 62° B. naphtha and 
any satisfactory asphalt cement free from mineral matter, and 
of a consistency such as will allow the penetration, at 77 degrees 
Fahrenheit, of a No. 2 needle weighted with 100 grams, of not 
more than three (3) millimeters, and not less than two (2). 
The asphalt cement shall be dissolved while soft and warm, in the 
naphtha in such proportions that the resulting paint shall give a 
glossy surface after evaporation of the latter, but at the same 
time can be applied so as to form as thin a coating as possible. 
The proportions will vary, depending upon the temperature at 
which the paint is made, but shall be about 240 pounds of asphalt 
cement to 50 gallons, or one barrel, of naphtha. 

"The concrete foundation shall be carefully swept and thorough- 
ly cleaned of all foreign matter. The paint coat shall only be 
applied to it when the latter is absolutely dry and free from the 
slightest dampness, as otherwise it will not adhere. It should be 
used in such quantity that fifty (50) gallons will cover from 350 
to 400 square yards of the concrete surface. 

"No more of the surface of the foundation shall be painted than 
Qaiv be covered with asphalt surface mixture within a few hours after 



THE INTERMEDIATE COURSE. 29 

the application. Under no circumstances shall the paint coat be 
allowed to become in any way dirty, nor shall the surface mixture 
be permitted to be applied to such a coat more than five hours after 
the painting has been done. 

"Owing to the inflammability of naphtha, the paint shall be 
prepared at a distance from all fire or flame and shall be applied to 
the surface of the concrete with the same precautions." 

SUMMARY. 

In the preceding chapter it appears that the use of a so-called 
cushion coat — that is to say, the application of the surface mixture 
to the foundation in two courses instead of one — is usually unsat- 
isfactory and has generally been abandoned. The ordinary open- 
binder course has been shown to be defective, owing to its lack of 
stability, on heavy-traffic streets and the substitution for it of a 
compact binder has been recommended, or, where economy is 
desired, the use of a paint-coat to tie the surface mixture to the 
foundation. 

An open binder course of this description will no doubt con- 
tinue to be very generally an element in the construction of the 
majority of asphalt pavements which are subjected to only mod- 
erate traffic. 



PAET II. 

THE MATERIALS CONSTITUTING THE ASPHALT 
SURFACE MIXTURE. 



CHAPTER III. 
THE MINERAL AGGREGATE. 

The asphalt surface, which directly carries the traffic and 
which is intended to withstand the wear and tear of the same and 
the action of the elements, is composed of a mineral aggregate 
and an asphalt cement, that is to say, it is an asphalt mortar 
or concrete. 

The mineral aggregate consists of sand, in exceptional cases 
also of stone, and a fine mineral dust or filler. 

The asphalt cement consists of a native hard asphalt, or some 
hard residue from an asphaltic oil or maltha, softened to the 
proper consistency by some heavy petroleum oil, generally the 
residual product of the distillation of petroleum. 

Before considering surface mixture as a whole the constituents 
which enter into its composition must be examined individually 
and the variations which are met with in them noted. 

The Mineral Aggregate. — Sand — Sand is the detritus of rock, 
consisting of particles smaller than gravel and larger than silt, 
and produced either by natural causes such as weathering and 
water action or by the hand of man in crushing rocks mechanically. 

Natural sand is the detritus, generally, of crystalline rocks 

30 



THE MINERAL AGGREGATE. 31 

and commonly water borne and water worn, in which quartz 
usually predominates, although calcareous sands, and those com- 
posed entirely of feldspar or largely of other silicates, are known. 

Artificial sand consists of the particles, produced in the process 
of crushing rocks, which are of corresponding size to those which 
make up natural sands. 

Sand is the principal constituent of asphalt pavements, and 
as such demands careful attention and study. Mr. A. W. Dow has 
remarked in a paper before the Society of Municipal Improvements 
in 1898: 

"As sand is 90 per cent of the pavement, why should it not 
be the most important ingredient to consider; and when a pave- 
ment is at fault, why should it not be more responsible than the 
asphalt which now bears the brunt of all failures?" 

As a matter of fact it is now pretty well known that, even 
if all the other constituents of an asphalt surface mixture are 
of the best, the wearing surface will not prove a success unless 
the sand is suitable for the purpose. 

In the early days of the asphalt-paving industry but little 
attention was given to the subject and the sand in use was what- 
ever happened to be the most available at the particular locality 
where work was being done. Later, opinions varied as to whether 
a coarse or a fine sand was more desirable, and there was a vibration 
from one to the other, together with equally wide variations in 
the consistency of the asphalt cement. In 1890 we find an expert 
of that day stating that he is " pretty well convinced that sand 
and matter that passes the 60 mesh ought not to enter the mix- 
ture "; and again in 1892 ; having examined "ten old pavements 
that have withstood wear," saying: "taking these results [of his 
analyses] on the face of it, it is observed that in general the sand 
used was on the fine side." No definite conclusions were drawn 
at that time as to what a desirable sand was. 

To-day we are better informed as to the best sand for a good 
surface mixture, but unfortunately we know too little in regard 
to the cause of the varying character of the particles composing 
the quartz sand which is used. We have not been able to tell 
why a certain Missouri River sand produces such a mushy mixture 



32 THE MODERN ASPHALT PAVEMENT. 

and is so unsatisfactory that its use has had to be abandoned, or 
why a Platte River sand is possessed of peculiarities seen in that 
from no other river. 

Difference in the shape of the grain and in the character of 
its surface are the probable causes, and these characteristics of 
a sand are, therefore, probably next in importance to the composi- 
tion and size of the grains in determining its suitability for paving 
purposes. 

Sorby, 1 who has studied the subject of sands carefully, has 
classified them as follows: 

" 1. Normal,- angular, fresh-formed sand, such as has been 
derived almost directly from the breaking up of granite or schistose 
rocks. 

" 2. Well-worn sand in rounded grains, the original angles being 
completely lost and the surfaces looking like fine-ground glass. 

" 3. Sand mechanically broken into sharp angular chips, show- 
ing a glassy fracture. 

"4. Sand having the grains chemically corroded, so as to pro- 
duce a peculiar texture of the surface, differing from that of worn 
grains or crystals. 

" 5. Sand in which the grains have perfectly crystalline outline, 
in some cases undoubtedly due to the deposition of quartz upon 
rounded or angular nuclei of ordinary non-crystalline sand." 

In the paving industry all these sands have been met with, 
but grains of several kinds not mentioned by Sorby are frequently 
found. From an examination of several hundred sands from dif- 
ferent localities the writer has been able to classify them, according 
to their source, by peculiarities of composition, by the shape, and 
by the surface of the grains, as follows: 

Classification of Sand. 
Source: 

Commercially. 
1. Beach sand. 
Seashore. 
Lakeshore. 

»Q. J. Geol. Soc, 1880, 36, 58. 



THE MINERAL AGGREGATE. 

2. River sand. 

3. Bank sand. 

4. Sand derived from soft sandstone. 

5. Artificial sand. 

Or with especial reference to their physical origin. 

1. Beach sand. 

Marine — tidal action and sorting. 
Lakeshore — storm action and sorting. 

2. Alluvial sand. 

Subaqueous, recent. 

Stream. 

Lake. 
Bank or pit deposits. 
Glacial, stream, lake, etc. 

3. iEolian sand. 

Dune. 
Loess. 
Volcanic. 

4. From sandstone. 

5. Crushed stone. 

Composition: 
Silica. 
Quartz. 

Hard clear. 

Soft cloudy. 

Ferruginous. 
Silicates. 

Shales and schists. 

Feldspar. 

Hornblende, Pyroxenes. 
Calcareous. 

Limestone. 

Carbonates. 

Shell. 

Coral. 



34 THE MODERN ASPHALT PAVEMENT. 

Mixed composition. 

Various kinds of quartz. 
Quartz and silicates. 
Quartz and carbonates. 
Quartz and shell. 

Shape: 

Irregular. 

Sharp angles. 

Rounded angles. 
Oval. 

Worn by water action. 
Round. 

River. 

Glacial. 

Rock. 
Crystalline. 

Surface : 

Sharp, original or fractured surface, not at all or little 

worn. 
Slightly worn on edges. 
Smooth and polished "soft sand." 
Smooth and with surface like ground glass. 
Covered with cementing material. 
Acted upon chemically. 
Porous, coral sand, limestone sand, shells. 

Size of grains : 
Uniform. 

Particles distributed in size, well graded. 
Quicksand. 

These different classes of sand may be described with special 
reference to their use in the asphalt industry. 

Beach Sands. — Seashore. — These are little used because as a 
rule they are so sorted by currents of more or less uniform hydraulic 
value that they are too much of one size. For example, a sand 
found on Rockaway Beach, Long Island, is made up of grains 
passing the following sieves: 



THE MINERAL AGGREGATE. 



35 



Passing 200-mesh sieve 0% 



100- 


a n 


80- 


1 1 ( e 


" 50- 


1 1 (i 


40- 


t i it 


30- 


(i i c 


20- 


<< it 


" 10- 


a u 



7 
32 
57 
2 
1 
1 


100 



It appears that 89 per cent of all the particles in the sand are 
of 50- and 80-mesh size. The tidal currents are such that par- 
ticles of smaller size are washed away while the larger ones 
have been left behind in the movement of the beach sand to its 
present location. 

As far as character of the grain is concerned beach sands often, 
and in fact in most cases, could not be improved upon. Fig. 2, 
No. 1. 

The most remarkable seabeach sands in the United States 
are found on the eastern coast of Florida. They consist, on the 
beaches of the northern part of the State, of pure white quartz 
grains which have a fresh and angular fracture. Further south, 
as at Lake Worth Inlet, they are made up of quartz and shell 
fragments of about the same size. The grains are much coarser 
owing to local conditions. Fig. 2, No. 2. 

An explanation of the presence of quartz sand at a point so 
far distant from any rock formations which contain this material 
can only be arrived at by assuming that this mass of sand has 
been transported down the coast by tidal action and ocean currents. 



No. 30516 — Lake Worth Inlet; bar sand; about 6 miles from Palm Beach, 
Florida. 
' 30534 — St. Augustine; north beach; from dunes 10 to 15 feet high. 
30535 — . ' ' " " " along high-water line ; river side. 

30536—" " " " " " " ocean side. 

30547— St. John's Bluff. 
'' 30546 — Mayport, Duval County; from 1 mile south of Mayport, I mile 

from ocean. 
" 30548 — Mayport, Duval County; from sand-dunes 10 feet high. 



36 



THE MODERN ASPHALT PAVEMENT. 



Test number 


30516 


30534 


30535 


30536 


30547 


30546 


30548 


Passing 200-mesh 
100- " 
80- " 
50- " 
40- " 
30- " 
20- " 
10- " 


0% 

1 

1 
16 
40 
22 
15 

5 


1% 
45 
41 
12 

1 








1% 
31 
50 
17 

1 








1% 
32 
50 
16 

1 








1% 
18 
39 
26 
10 

2 

2 

2 


2% 

6 
20 
39 
19 

8 

4 

2 


1% 
39 
50 

9 

1 










100 


100 


100 


100 


100 


100 


100 


Retained 10- " 
Soluble in HC1. . . 


.4% 
45.9% 


1.5% 


2.7% 


— 


1.1% 

•8% 


2.0% 

1-2% 


— 



The above sands are all pure quartz with the exception of 
sample No. 30516 from Lake Worth Inlet, which contains 45.9 
per cent shell detritus. 

The beach sands of Cuba, to the west of Havana, are composed 
entirely of small shell fragments, while those on the south coast 
to the east of Santiago are either coral or, in Daiquiri Bay, largely 
of hard silicates, the particles being transparent and of the rich 
color of hornblende. 

Seabeach sands are reputed to be far from sharp, but among 
many recently examined for their suitability for use in the paving 
industry most of them have proved sharper than river or bank 
sand. Fig. 2, No. 1. 

Beach Sands. — Lakeshore. — Another form of beach sand is 
found on the shores of the numerous lakes near some of our large 
cities, the great lakes in the North, and Lake Pontchartrain in 
the South. 

The assorting of the particles composing lakeshore sands is 
accomplished largely by the movement of water produced by 
storms, a more complicated one usually than is presented on the 
seabeaches, although not as powerful as a rule. Tidal action is 
of course absent. In many localities the force of the waves or 
of the induced currents are so small as to permit of the deposition 
of very fine sand or of that in which the particles are very well 
graded in size. In other cases there is a great similarity between 
lake and seabeach sands. The remarkable variation in the size 




Fig. 2. — Sand Grains- 



37 



38 



THE MODERN ASPHALT PAVEMENT. 



of lakebeach sand, even on beaches within a few miles of each 
other, is illustrated by the following examples: 



Lake Michigan. 



Kenosha, Wis. 
1899. 



Chica-o, 111. 
1897. 



Lake Erie. 



Sandusky, 
Ohio. 



200-mesh sieve. 
100- 

80- 

50- 

40- 

30- 

20- 

10- 



2% 



16 

52 

13 

3 

2 

4 

100 



10% 

68 

15 

3 

3 

1 





100 



o% 
11 

23 

24 
32 

7 
2 
1 

100 



In the Kenosha sand, although the uniformity of grade is not 
carried as far as was the case on Rockaway Beach, 52 per cent 
of the particles are of a size to pass a sieve of 50 meshes to the 
inch. And, again, we have finer sand from near Chicago of still 
greater uniformity. On the other hand, near Sandusky a lake 
sand is available which is of quite varied size of grains. Here the 
sorting of the sand particles has been limited and the grading 
is satisfactory for use in asphalt surface mixtures without modi- 
fication. Where lake sands are of too uniform size two or more 
sources of supply may be used and mixed in suitable proportions. 
Other typical beach sands from Lakes Michigan, Erie, and Ontario, 
which are in the writers' collection, sift as follows : 





Milwaukee 
Beach. 


White Fish 
Bay, Wis. 


Lake 
Ontario. 

1894. 


Lake 

Pontchar- 

train. 


Lake Erie. 

1892. 


Passing 200-mesh 


o% 


1% 


1% 


o% 


2% 


100- " 


2 


27 


2 





29 


80- " 


6 


32 


46 


1 


14 


50- " 


32 


32 


44 


28 


47 


40- " 


22 


3 


3 


47 


4 


30- " 


14 


2 


2 


21 


2 


20- " 


14 





1 


3 


2 


10- " 


10 


3 


1 










100 


100 


100 


100 


100 



THE MINERAL AGGREGATE. 39 

The very considerable variations in the size of these sands 
from different sources make it possible, however, by mixing those 
of different sizes ; to produce a sand of any grading that may be 
desired for a surface mixture, and that, too, without great labor. 

A peculiarity of lakebeach sand is the rapidity with which 
all the sand, which may be of most desirable character for asphalt 
work, may be removed from any particular locality by a violent 
winter storm and its place taken by a sand of quite different grad- 
ing. This is of common occurrence between Chicago and Mil- 
waukee, and no doubt elsewhere, so that the fact that a suitable 
sand can be found at a particular point during any one working 
year does not mean that the sand will be of the same grading 
another year, especially if the storms of an intervening winter 
have been heavy. The variation in the available sand from year 
to year in this way makes a decided difference in the character 
of the asphalt mixture turned out at different times in cities which 
are dependent on such a source of supply. 

Lakebeach sands, originating at old lake levels, may, like 
alluvial sands, be found at times in banks or pits where changes 
of lake levels, which are so frequent in geological time, have left 
them above the elevation of, and at times far distant from, the 
present water level. For commercial uses these cannot be dis- 
tinguished from beach sands of more recent origin. 

Alluvial Sands include all those which have been moved by 
and deposited from running water as distinguished from beach 
sands. They may be found to-day in the beds of streams or along 
their shores and in banks and pits where they have been left by 
running water in past geological times. Alluvial sands may 
also include those originating in glacial streams and occurring 
both in banks and pits and as reassorted by recent water action. 
There are also deposits in lakes from streams flowing into them 
which need not enter into our consideration, being rarely so avail- 
able as to be of technical importance. 

River Sands. — As river sands are conveniently considered 
those which are found in the beds of streams or on their beaches, 
and which are still largely subject to the action of water. They 
are oftener found at the concave side of some bend or at a place 



40 THE MODERN ASPHALT PAVEMENT. 

where the current makes a change in direction or loses its force. 
Geikie describes the deposition of river sand as follows: 

" While the main upper current is making a more rapid sweep 
round the opposite bank, under currents pass across to the inner 
side of the curve and drop their freight of loose detritus, which, 
when laid bare in dry weather, forms the familiar sand-bank or 
shingle-beach. Again, when a river well supplied with sediment 
leaves mountainous ground where its course has been rapid and 
enters a region of level plain, it begins to drop its burden on the 
channel.' ' 

River sands are usually obtained by dredging and are thus 
distinguished from bank or pit sand, which are worked from dry 
deposits. They are most varied in character and form an impor- 
tant part of the supply in use in asphalt paving. In each river 
they seem to have distinguishing peculiarities, and in no two cities 
having their source of sand in a river bottom is the supply of 
the same character, while for any one city the supply may vary 
in character from year to year. 

This may be due to two causes : to the different nature of the 
rock formations from which the sand found in different rivers 
is derived and to the different physical conditions to which the 
debris from these formations has been exposed, resulting in pecu- 
liarities of shape, size, surface, etc. 

River Sand at Kansas City and Washington, D. C, etc. — River 
sands are or have been in use in Washington from the Potomac, in 
Kansas City from the Missouri and from the Kansas, in Omaha 
from the Platte, and in St. Louis from the Mississippi and Missouri. 
No two of the sands resemble each other in their behavior in an 
asphalt surface mixture. The peculiarities which each one shows 
can be described, but as yet it is impossible to show why they 
all differ so much in their adaptability to making a desirable 
surface mixture. 

In one of these cities for many years river sands were in use 
in the surface mixture without the fine bank sand now mixed 
with it. The river sands would not carry a sufficient percentage 
of asphalt and made a surface which marked badly under traffic, 
perhaps more from their coarseness than from other reasons, but 
which, in comparison with the coarse Washington mixtures of 



THE MINERAL AGGREGATE. 



41 



Potomac River sand, which do'not mark in the same way, shows 
a decided difference in character, not due to the size of the particles 
of which it is composed. 

Two typical surface mixtures from the two cities will illustrate 
the difference due to the sand. A street in the western city marks 
up more than most of the pavements in that town, that is to say, 
badly. The average mixture laid in Washington in 1894 with 
a straight Potomac River sand scarcely marked at all. The com- 
position of these two mixtures is as follows: 





Kansas 
City, 1893. 


Washington, 

1894. 


Bitumen 


9-9% 

9.0 

6.3 

5.4 
36 .3 
10.8 

8.2 

6.5 

7.6 


10.9% 
9.9 


Passing 200-mesh sieve 


" 100- " " 


1.5 


" 80- " " 


3.7 


" 50- " " 


16.1 


" 40- " " 


28.9 


" 30- " " 


20.7 


" 20- " " 


5.9 


" 10- " " ..» 


2.4 








100.0 


100.0 



It would be natural to expect that the Washington mixture 
with the higher percentage of bitumen and coarser sand would 
be the softer and mark more than the western mixture, but that 
is not the case. With a grading not far different and apparently 
less favorable, the Potomac sand will carry 1 per cent more bitu- 
men than that in use in the West and still not mark in hot weather. 
The possible difference in sands from different rivers is well illus- 
trated in this case. 

As striking differences are to be seen between the mixtures 
made with river sand in two western cities, which may be denoted 
No. 1 and No. 2. It is not difficult to get sands in either city which 
can be properly graded to our present accepted standard and 
which, it would be supposed, from all appearances would make 
equally excellent asphalt surface mixtures. On making the mix- 
tures, however, it is found that the river sand at city No. 1 would 
not hold the usual amount of asphalt cement and that the varia- 
tions in amount from one box of mixture to another was so great 
as to make any uniformity in working impossible. 



42 



THE MODERN ASPHALT PAVEMENT. 



River Sand at City No. i. — In* 1896 an attempt was made to 
devise a satisfactory mixture for work in this city. A coarse 
sand was obtained from one river and a fine sand from another. 
They had the following mesh composition: 



Passing 200-mesh sieve 


0% 

5 
11 
42 
20 
16 

4 

2 

100 


19% 
42 
19 
18 

2 







100 




" 100- " " 




80- " " 

" 50- " " 




" 40- " " 




" 30- " " 




" 20- " " 




" 10- " " 









These sands were combined in such proportions as to make a 
suitable grading and asphalt cement added until the paper test * 
showed a suitable amount. The mixed sand would hold at 
the most but 142 pounds of asphalt cement to the 9-foot box of 
material, and would frequently carry only 126 pounds, and yet 
the mixture was very sloppy, where a New York mixed sand, 
weighing about the same per cubic foot, would carry over 160 
pounds and stand up firmly. 

The grading of the western sand and that from New York, 
for comparison, was as follows: 





City No. 1. 


New York. 


Passing 200-mesh sieve 


4% 
12 
14 
37 
13 
10 

5 

5 

100 

846 
94 
126-142 

13.0-14.0 


6% 
12 


" 100- " " 


" 80- " " 


12 


" 50- " " 


26 


" 40- *' " 


24 


" 30- " " 


8 


" 20- " " 


7 


" 10- " " 


5 


Weight per 9-foot box, lbs 


100 

875 


" " cubic foot, lbs. 


97 


A. C. per box, lbs. „ 


163 


Per cent Trinidad A. C. in mixture 


15.7 



1 Pages 352-356. 



THE MINERAL AGGREGATE. 



43 



It is impossible at present to explain the difference between 
the two sands, but it must be one of shape and surface of the grains 
rather than of volume per cent of voids, there being no great 
difference between them in this respect. 

The use of these sands was abandoned for the reasons which 
have been given, although the work done with the mixture made 
at that time has been fairly satisfactory. Such a mixture required 
too much watching owing to the rapid changes in proportions 
which were necessary. The experience has proved, however, very 
instructive and has shown that many mushy mixtures do not 
prove as bad under traffic as they look when hot, but may give 
good service; and that the asphalt cement with such sand may be 
held at a point as shown by the paper stain, which with sand 
from other sources would be dangerous. 

Later, the sands in use in this city were both taken from the 
same river, one being a coarse sand and the other finer. They 
have been carefully selected by the yard foreman, who has gone 
out with his sieves on the dredge and taken only sand of a certain 
grade. 

Typical specimens of these river sands sift as follows: 





Coarse. 


Fine. 




1896. 


1899. 


1898. 


1899. 


Passing 200-mesh sieve 
" 100- " 
80- " 
50- " " 
40- " 
30- " 
20- " 
10- " 


2 

.. 26 

.. 42 

.. 11 

6 

8 

4 


1% 

5 
21 
28 
20 
10 

9 

6 


2% 

4 
22 
28 
19 
10 
10 

5 


20% 
24 
33 
17 

3 

1 

2 




17% 
40 
30 
10 

1 

1 

1 




25% 
42 
21 
10 

1 

1 








100 


100 


100 


100 


100 


100 


Retained on 10-mesh si< 


3ve 4% 













44 THE MOOERN ASPHALT PAVEMENT. 

And the mixed sands as coming from the hopper: 



Passing mesh. . 

1898 . ... 

1899 



200 


100 


80 


50 


40 


30 


20 


10 


9% 


14% 


30% 


28% 


7% 


4% 


5% 


3% 


6 


10 


25 


36 


9 


7 


3 


4 


10 


9 


25 


9 


16 


11 


9 


11 


13 


13 


18 


22 


15 


9 


6 


4 


5 


7 


18 


27 


21 


9 


9 


4 


17 


13 


17 


18 


15 


9 


7 


4 



= 100% 
= 100 
= 100 
= 100 
= 100 
= 100 



The sands in 1898 and 1899 carried from 154 to 165 pounds 
of asphalt cement to the 9-foot box and are more satisfactory than 
those previously in use on account of their greater regularity. 
The later mixtures have averaged in composition as follows, which 
may be compared with that made formerly with the unsatisfactory 
sand : 





Earlier Sand. 


Later Sand. 
First Year. 


Later Sand. 
Second Year. 


Bitumen 


9.9% 
14.3 

9.4 
13.3 
33.0 
10.3 

6.1 

2.6 

1.1 


11.3% 
13.2 

9.7 
14.7 
37.2 

5.7 

3.8 

2.7 

1.7 

100.0 


10.4% 

13.0 

10.0 


Passing 200-m 
' ' 100- 


ssh sieve 


" 80- 


i n 


9.0 


50- 
" 40- 

30- 
" 20- 


i it 
i a 
t tt 
i it 


25.0 

15.0 

8.0 

6.0 


" 10- 


t tt 


4.0 










100.0 


100.4 



The second mixture of the year 1899, was the most satisfactory 
of any made up to that time, but even here undesirable features 
are to be found, which will be considered later. 

The peculiarities of these sands are, however, very instructive 
if at the same time very trying in the asphalt business. 

River Sand at City No. 2. — In city No. 2 the river sand presents 
a most desirable grading, as shown by the following sifting of some 
in use in July, 1899: 



THE MINERAL AGGREGATE. 



45 



Passing 200-mesh sieve 


3% 
26 
12 
39 
14 

2 

3 

1 

100 


2% 
19 


' ' 100- " " 


80- ' ' " 


19 


50- " " 


41 


" 40- " " 


12 


" 30- " " 


3 


" 20- " " 


2 


" 10- " " . 


2 
100 



This sand is peculiar, however, in that in making a mixture 
according to our practice it is found that if the asphalt cement 
is added in amount only sufficient to stain the paper 1 to the 
same degree as with the sands in other cities, the bitumen in the 
mixture does not exceed 9 per cent. With a larger amount of 
asphalt cement, sufficient to yield 10 per cent of bitumen in the 
mixture, the latter is very sloppy. 

This peculiarity might lie either in the heavier volume weight 
of the sand and the smaller voids or in some characteristic of the 
surface of the grain which would prevent the usual amount of 
asphalt cement from adhering to it. It has been found, however, 
on the use of this same sand in a neighboring city that a satis- 
factory surface containing as much as 10 per cent of bitumen can 
be laid by making the mixture as rich as is necessary for this figure, 
and disregarding the usual indications of richness and overfill- 
ing of the voids. The finished surface does not appear to be exces- 
sively soft in summer and wears well. This would point to the 
correctness of the idea that the peculiarity of this sand lies in its 
surface and perhaps in its shape. Nothing peculiar in either of 
these respects, as far as can be seen under the microscope, can be 
discovered, the sand being a nearly pure quartz, having a ground- 
glass surface with rounded angles. Fig. 2, No. 3. 

In considering the subject of mixtures these peculiar sands 
will be referred to again. 2 



1 This paper test will be described later, pages 352-356, 514. It indicates 
the amount of asphalt the sand will carry. 

2 Page 351. 



43 THE MODERN ASPHALT PAVEMENT. 

The river sands of the United States in the Mississippi Valley 
seem, therefore, to be possessed of peculiar properties which we 
are unable as yet to account for, and it is necessary to handle 
them in the paving industry in a different way from other sands, 
or else to reject them. 

Bank or Pit Sands. — Bank or pit sands are deposits of sand 
which have been laid down in their present position by various 
agencies in past geological times, as distinguished from the river 
and beach sands, which have been described and which are the 
results of the recent assorting of detritus by water action, or by 
the reassorting of bank sands under changed conditions, which 
is quite possible, as on the north shore of Long Island, where the 
glacial bank sands are often reassorted by water action into modern 
beach sands. 

Bank sands are of the most varied derivation — river, beach, 
glacial, aeolian, etc. — including all possible sources of origin. On 
the Hudson are found banks of river sand, as at Croton ; on Long 
Island banks of glacial sand, as at Cow Bay, and in Sioux City, 
Iowa, banks of seolian sand in the loess. 

Bank sands grade in size from fine gravel or coarse concrete 
sand to the impalpably fine ones which are found in those wind- 
blown deposits of a large portion of the West, called loess, and 
which are often almost entirely a sharp sand composed of quartz 
particles fine enough to pass a 200-mesh sieve. 

To the paving industry the bank sands offer sources of sup- 
plies which are more varied in the size of the particles of which 
the sand is made up than the river and beach sands of recent 
origin, and are oftener to be obtained of that degree of fineness 
which has been found to be such an essential feature in our modern 
mixtures, that is to say, of 80- and 100-mesh size. The varied 
grading of different bank sands, not including the coarser con- 
crete supplies which are not used in the asphalt industry for sur- 
face mixture, is . illustrated by the following characteristic speci- 
mens (see table, p. 47). 

These bank sands, it will be seen, admit of combinations of two 
or more in such a way as to attain any required grading. Fortu- 
nately no bank sands are met with which present any of the pecu- 



THE MINERAL AGGREGATE. 



47 



liarities of the river sands of the Mississippi River Valley. They 
all carry asphalt well and make good mixtures. 





New York Supply, 1899. 


Boston Supply. 


Passing Sieve 
of Meshes. 


Cow Bay. 


Corbin's 

Bank, 

Steinway. 


Delagoa 

Bay 
Ballast. 


Brain tree, 

Mass. 


Canton, 

Mass. 


200 
100 
80 
50 
40 
30 
20 
10 


4% 

7 

9 
28 
22 
15 

9 

6 

100 


2% 

5 

7 
24 
16 
18 
13 
15 

100 


6% 
10 
12 
28 
15 
13 
10 

6 

100 


1% 
60 
36 

2 

1 







100 


12% 
25 
15 
29 

9 

6 

2 

2 

100 


7% 
13 
14 
33 
19 

6 

6 

2 

100 





Buffalo 

Supply, 

Attica, N. Y. 


Elmira 
Supply. 


Utica Supply. 


Lafayette 
Supply. 


Toronto, 
Ontario, 
Supply. 


200 


32% 


6% 


8% 


3% 


29% 


100 


29 


7 


31 


5 


36 


80 


17 


38 


25 


4 


14 


50 


19 


48 


20 


36 


13 


40 


1 


1 


12 


37 


2 


30 


1 





2 


10 


6 


20 


1 





1 


3 





10 








1 


2 







100 


100 


100 


100 


100 





Kent, England, Glacial. 












Louisville Bank. 


Sioux City, 










White. 


Yellow. 






200 


o% 


tr. 


48% 


99.5% 


100 


11 


4% 


20 


.5 


80 


74 


28 


11 




50 


14 


62 


18 




40 


1 


6 


1 




30 


tr. 


tr. 


2 




20 













10 


























<■» 


100 


100 


100 


100.0 



48 1HE MODERN ASPHALT PAVEMENT. 

M&ny fcatik sands are unsuitable for use in the surface mixture, 
however, owing to the presence of too much clay or loam, or to a 
surface on the grain which is more or less covered with a ferru- 
ginous cement, existing in the original rock from which the sand 
is derived, or with argillaceous matter, to neither of which surfaces 
does asphalt adhere satisfactorily. The former peculiarity is of 
the commonest occurrence, but probably only becomes serious 
when the amount of clay or loam is too large to be taken care of 
as dust, or is in such a form as to ball up in the sand-heating 
drums, or not to mix with the asphalt cement properly. A loamy 
tempering sand has been in use successfully in an Ohio River 
city for several years. The latter difficulty is typical of the red 
sands of New Jersey, which have a coating of iron oxide firmly 
adherent to their surfaces, and the sands found associated with 
the London gravels which are similarly but not so distinctively 
coated. From the latter sand a coating of asphalt cement would 
wash off in a few weeks when exposed to the weather, destroying 
the surface mixture made with it. The red sands of New Jersey 
may possibly be used without danger; that from Rutherford has 
been as a tempering sand, but they do not look attractive and 
are suspicious. 

There are no other noticeable peculiarities of bank sands to 
be mentioned which, as far as is known, render them unsuited 
for surface mixtures, except the presence of too much 200-mesh 
material which consists of sand grains of that size and not dust. 
Sand of this size is, as a rule, disadvantageous in a mixture and 
makes it mushy and liable to push or shove under traffic. The 
peculiarities of mixtures containing much 200-mesh sand will be 
discussed later. 

Quicksands. — Any of the preceding sands is often called quick- 
sand if it is very fine. Quicksands are really of that peculiar 
nature only when they consist of particles largely finer than will 
pass a sieve of 200 meshes to the inch and consequently having 
a small hydraulic value. When such sands have their voids filled 
or more than filled with water they are unstable and mobile. There 
is no reason why a coarse sand should not at the same time be a 
quicksand if it is supported and its voids more than filled by a 



THE MINERAL AGGREGATE. 49 

force of water of sufficient head. It has often been stated that 
quicksands consist of uniform sized and round particles, but recent 
examination of some material of this description 1 has shown that 
they generally consist of sharp grains and are often well graded. 
Several quicksands have been examined by the writer with the fol- 
lowing results, which are characteristic of such material : 

QUICKSANDS— BOSTON, 1897; WORCESTER, 1900. 
Test No. 11541. Boston — Neponset Valley Sewer. Nat. Contr. Co. 

a a ii {-a o i ( t ( < ( a it 1 1 tt 

it tt H544 *< < ( << i( << << << 

" " 30723. Worcester— Green Street. H. P. Eddy. 
" " 30724. " " " " " " 

11 il 30725. " " " " " " 

Finest-ground limestone, all passing 200 mesh. 

Nos. 11541, 11542, and 30725 are clean sands, grains all sharp. Nos. 
11544, 30723, and 30724 contain a small amount of clay, less than 1 per cent, 
not subsiding entirely in one week. 



Test Nos. 



Voids in hot com- 
pacted sand. . . 

Weight per cubic 
foot of same in 
pounds 



Sieve. 



200 
100 
80 
50 
40 
30 
20 
10 



Diameter, 
Milli- 
meters. 

.035 

.065 

.09 

.17 

.23 

.31 

.50 

.67 
1.00 
2.00 



Greater 
than 2. 



11541 

29.3% 
117.2 



19.2% 

7.9 
18.9 
34.0 
11.0 

7.0 

1.0 

1.0 



100.0 



11542 



11.2% 
14.2 
19.6 
22.0 

8.0 
16.0 

4.0 

2.0 

2.0 

1.0 



100.0 

2.0% 



11544 

40.2% 
99.1 



65.5% 

13.7 

17.8 

2.0 

1.0 



100.0 



30723 
36.7% 



30724 

34.7% 



1C3.8 106.1 



47.2% 
19.6 
11.2 
13.0 

4.0 

3.0 

1.0 

1.0 



100.0 



11.6% 
11.4 

9.0 
39.0 
12.0 
10.0 

3.0 

3.0 

1.0 



100.0 



30725 



79.7% 
9.5 
9.8 
1.0 



100.0 



Finest- 
ground 
Lime- 
stone. 

39.3% 



100.4 



63.5% 

17.7 

18.8 



100.0 



1 Landreth, Wm. B., The Improvement of a Portion of the Jordan Level 
of the Erie Canal. Trans. Am. Soc. C. E., 1900, 43, 596. 



50 THE MODERN ASPHALT PAVEMENT. 

It is apparent that some quicksands are quite widely graded, 
others consist to a very large extent of uniform particles smaller 
than .035 millimeter in diameter (.0014 inch) and even finer than 
the finest dust in Portland cement. That they are all composed 
of sharp grains, contain traces only of clay or none, have an ex- 
traordinary fineness, in one case greater even than that of the 
best ground limestone, are their astonishing characteristics. 

The angularity of these small particles is explained by their 
small hydraulic value and consequent freedom from attrition, 
as shown by some experiments of Daubree, quoted by Geikie, 
Text-book of Geology, third edition, page 385. He says: 

"In the series of experiments already referred to, Prof. Daubree 
made fragments of granite and quartz to slide over each other 
in a hollow cylinder partially filled with water and rotating on 
its axis with a mean velocitiy of .80 to 1 metre in a second. He 
found that after the first 25 kilometers (about 15^ English miles) 
the angular fragments of granite had lost t 4 q- of their weight, 
while in the same distance fragments already well rounded had 
not lost more than y^ to jj r . The fragments rounded by this 
journey of 25 kilometers in a cylinder could not be distinguished 
either in form or general aspect from the natural detritus of a river- 
bed. A second product of these experiments was an extremely 
fine impalpable mud, which remained suspended in the water 
several days after cessation of the movement. During the pro- 
duction of this fine sediment the water, even though cold, was 
found in a day or two to have acted chemically upon the granite 
fragments. After a journey of 160 kilometers, 3 kilograms 
(about 6^ pounds avoirdupois) yielded 3.3 grams (about 50 
grains) of soluble salts, consisting chiefly of silicate of potash. 
A third product was an extremely fine angular sand consisting 
almost wholly of quartz, with scarcely any feldspar, nearly the 
whole of the latter mineral having passed into the state of clay. 
The sand grains as they are continually pushed onward over each 
other upon the bottom of a river become rounded as the large 
pebbles do. But a limit is placed to this attrition by the size 
and specific gravity of the grains. As a rule the smaller particles 
suffer proportionately less loss than the larger, since the friction 



THE MINERAL AGGREGATE. 51 

on the bottom varies directly as the weight and therefore as the 
cube of the diameter, while the surface exposed to attrition varies 
as the square of the diameter. Mr. Sorby ; in calling attention to 
this relation, remarks that a grain y^ of an inch in diameter 
would be worn ten times as much as one T -Jo of an inch in diameter, 
and a pebble 1 inch in diameter would be worn relatively more by 
being drifted a few hundred yards than a sand grain T oV o °f an 
inch in diameter would be by being drifted for a hundred miles. 
So long as the particles are borne along in suspension, they will 
not abrade each other, but remain angular. Prof. Daubree found 
that the milky tint of the Rhine at Strasburg in the months of 
July and August was due, not to mud, but to a fine angular sand 
(with grains about / T millimeter in diameter) which constitutes 
To itWo" °f the total weight of the water. Yet this sand had 
travelled in a rapidly flowing tumultuous river from the Swiss 
mountains, and had been tossed over waterfalls and rapids in its 
journey. He ascertained also that sand grains with a mean diam- 
eter of T V mm. will float in feebly agitated water, so that all 
sand of finer grains must remain angular. The same observer has 
noticed that sand composed of grains with a mean diameter of 
% mm. and carried along by water moving at a rate of 1 metre per 
second is rounded and loses about to oW °f its weight in every 
kilometer travelled." 

These remarks explain some of the characteristics of the quick- 
sands which have been described. 

So-called quicksands consisting largely of particles ' of 100- 
and 80-mesh size form one of the most valuable sand supplies which 
can be used in the paving industry. They are known as temper- 
ing sands, and when mixed with the ordinary sand produce a 
grading which is more satisfactory than that of any sand deficient 
in such fine particles. 

Glacial Sand. — Such sands are found on the north shore of 
Long Island and are largely used in the paving industry in the 
city of New York. Fig. 2, No. 4. 

In those parts of the country which were covered with the 
ice sheet during the Glacial Period a large part of the beach, lake, 
and river sands may consist of glacial material reassorted by 



THE MODERN ASPHALT PAVEMENT. 



more recent water, action, but this is, of course, not true of sands 
from regions south of the terminal moraine, nor is it probably 
the case with the sands found in our western rivers, which are 
of very recent origin. This may account for the fact that the 
sands from the Mississippi and Missouri Rivers and their tribu- 
taries are so different from many other river sands. 

Sands Derived from Sandstones. — Supplies of sand are to be 
found at times which are obtained by grinding and breaking down 
loose sandstones of little coherence. These sands are largely used 
in glass-making and are usually very fine quartz. They have 
been offered in several cities for paving purposes. Two samples 
sifted as follows: 



Passing 200-mesh sieve 


5% 

7 
13 
45 
25 

2 

1 

2 

100 


5% 
15 
22 


100- " " 

11 80- " " 


" 50- " " . 


40 


" 40- " " 


15 


1 ' 30- " " 


1 


" 20- " " 


1 


" 10- " " 


1 




100 



They have never been utilized in the paving industry. 

Artificial Sands. — The finer material produced in crushing 
rock for the purpose of obtaining broken stone for concrete when 
screened to a proper size is a sand. It differs essentially from 
the natural sands in that it has not been subjected to weathering 
or attrition and consequently is sharp and has a rough surface. 
Fig. 2, No. 5. It is generally well graded through different 
sizes and has low voids. Specimens of such a sand are represented 
by the screenings from the crushing of granite, gneiss, limestone, 
and trap in various parts of the East, which sift as follows: 

Test No. 68417. Crushed gneiss screenings from Jerome Park Reservoir, 
New York. 
" " 66563. Trap-rock screenings, Nyack, N. Y. 
" " 62082. Limestone screenings, Muskegon, Mich. 
" " 64840. " " Owosso, Mich. 

" " 69721. " " Harrisburg, Pa. 

" " Washington, D. C. 



THE MINERAL AGGREGATE. 



53 



Tes 
Pas 


t number 


. . 68417 


66563 
10.5% 


62082 

17% 


64840 
7% 


69721 

28% 




ssing 200-mesh sieve 


• • 6.5% 


21% 




100- " 


.. 7.5 


7.5 


3 


5 


12 


14 




80- " 


.. 5.0 


2.5 




4 


7 


8 




50- " 


.. 12.5 


7.0 




8 


13 


11 




t 40 _ " << 


.. 12.5 


4.0 




5 


9 


8 




30- " 


.. 8.0 


5.0 




5 


9 


6 




20- " 


.. 10.0 


5.5 




6 


11 


8 




t 10 _ a iS 


.. 8.0 


15.5 


52 


18 


11 


19 




i-inch 


.. 17.0 


34.0 


28 l 


42 





5 l 




x << 


.. 3.5 


8.5 












1- << 


.. 9.5 


0.0 












Retained on 1-inch siev 


e . 0.0 


0.0 














100.0 


100.0 


100 


100 


100 


100 



Retained on 10 mesh. 



These screenings are of excellent character for use in hydraulic 
concrete and have also been successfully made part of the mineral 
aggregate of surface mixtures, as the finer material which they 
contain is very desirable in localities where the particles of the 
same size are not found in the native sand. 

The screenings from the softer limestones of the middle and 
far West are not so desirable as a substitute for native sand, and 
no attempt has been made to use them in an asphalt-surface mix- 
ture as sand. When ground they form a most desirable filler, as 
they readily become impregnated with asphalt. 

Purchase of Sands. — In this connection it may be well to state 
that no sand is desirable for use in an asphalt-surface mixture 
which would be considered suitable for use in lime or cement mortar. 
It is therefore often difficult to explain to sand-dealers the kind 
of sand needed , in the asphalt industry and more often difficult 
to find it, as there is no demand for such sand from others and 
consequently little inducement to open up or develop pits or 
supplies of the proper kind. It is well usually to say, in asking a 
sand-dealer for sands for surface mixtures, that one wishes a sand 
that is too "soft" for any other use, and that one which is suitable 
for mortar would be of no value for pavements. 

Composition. — The composition of a sand, as long as the grains 
are hard, cannot seriously affect its availability for use in an asphalt- 



54 THE MODERN ASPHALT PAVEMENT. 

surface mixture or be a cause of defects in it. Soft-grained sand 
should be rejected when this is possible. The grains of a very large 
majority of all the sands in use in the asphalt industry, in fact 
of almost all natural sands, are composed of quartz, the silicates, 
feldspar, etc., being decomposed and removed from the detritus 
of the original rock by weathering or water action. The character 
of the quartz may vary largely, however. It may be a clear, trans- 
parent, hard quartz, a softer cloudy-white quartz, or an even softer 
ferruginous one. The two latter suffer more from attrition, have 
round forms and dead surfaces. Rarely sands are found which 
consist of a large proportion of silicates or of shales, although a 
small amount of magnetite and the harder pyroxenes are to be 
detected in most sands. Potomac River sand often carries 3 per 
cent of magnetite, and that from Siboney beach, which has been 
used in Santiago, Cuba, must consist fully half of hard silicates 
such as hornblende and similar minerals, which are, however, not 
unsuitable for paving purposes. A sand formed by weathering 
of a granite rich in feldspar on Cape Neddick in Maine is largely 
made up of coarse particles of feldspar, but it is not of any prac- 
tical importance. 

The sand found in the Mohawk and Hudson River Valleys 
from Poughkeepsie to Geneva consists largely of small oval and 
flat particles of shale, although some quartz is present. These 
sands are, of course, comparatively soft, but good work for light 
traffic has been done with them. 

Calcareous sands are rather unusual, except those derived 
from shells and the detritus of coral. Limestones weather out 
or dissolve too rapidly in water to permit of the formation of 
sand, although they are found to a certain extent in admixture 
with quartz sands at many points. 

Coral and shell sands are common in southern latitudes, as 
in Cuba and Bermuda, for instance. They are the softest sands 
that are met, usually crumbling under moderate pressure. Few 
particles finer than 80-mesh size are found in the coral sands, 
as these are readily washed away and dissolved. The shell sands 
of Cuba are firmer than the coral sands. 

Mixed sands composed of quartz and silicates, and quartz 



THE MINERAL AGGREGATE. 



55 



and carbonates, occur. Such include the more evenly propor- 
tioned Siboney beach sand and the shale sand of Northern New 
York. The lake sands often contain considerable carbonates 
in the form of shells, and a small amount is found in almost all. 
Determinations of lime in several supplies, made in 1896, gave 
the following results: 



Source of Sand. 


Per Cent CaO. 


Buffalo — lake 

New York — bank. . . 


9.3% 
2.2 

.8 

.2 

.2 


St. Louis — river 

Kansas City — river ) . . . 

Boston — bank 



Their presence has no injurious influence on the sand as far 
as its use in asphalt surface mixture is concerned. Asphalt cements 
probably adhere better to limestone than to silica or silicates, and 
in this way it may be desirable. 

It is sometimes of interest to determine how much or what 
percentage of a sand is in a condition soluble in strong acid, such 
as hydrochloric. The amount found in the sands mentioned 
above, which were examined for lime, was as follows: 



Source of Sand. 



Per Cent Iron 
Oxide and 
Aluminum. 



St. Louis — river. . . 
Kansas City — river. 
New York — bank. . 
Boston — bank. . . . 
Buffalo — lake 




In the ordinary run of sand this is small and of no importance. 
In some of the sands, like the red sands of New Jersey, it is indic- 
ative of a weakness in the material. 

Sands may often carry admixtures of substances which cannot 
be considered as part of the original material from which they 
have been derived but which are adventitious in some way or 



56 THE MODERN ASPHALT PAVEMENT. 

other. Clay and loam are the commonest substances and their 
presence is accounted for in two ways. Either they are inti- 
mately mixed with the sands in the deposits, as in the fine bank 
sand mentioned as being used for tempering purposes, or they 
exist in strata covering or adjacent to the sand and are unavoid- 
ably mixed with it in collecting the latter. If not adherent to 
the grain a small amount will act merely like the dust added to 
the sand before the asphalt cement, but if the clay or loam balls 
in the drums and is not screened out it may prove injurious. 
A clean sand is in any case probably more desirable, although 
satisfactory results have been obtained with many loamy ones. 

Organic matter in the shape of vegetable debris is sometimes 
found in sand. It is usually removed in screening the hot sand 
as it comes from the drums. If this is not possible and the amount 
remaining is excessive the sand should be rejected. 

Shape of Sand Grains. — The shape of the grains of which sands 
are composed is quite varied. 

Irregular Grains. — Fresh detritus from the original rock 
is generally irregular in shape and with sharp angles unless it is 
derived from a rock composed of grains which have already existed 
as sand. Sands formed of irregular grains are not common, but 
they are often found with the grain quite irregular in shape but 
the angles somewhat rounded by water or glacial action. The 
sands from the north shore of Long Island are of this class. Fig. 2, 
No. 4, shows the peculiarity of the grain. They are of very irregu- 
lar shape with re-entrant angles, but are slightly rounded with 
loss of the sharpness of the original fragment. 

Crystalline Grains. — Sands containing crystals are mentioned 
by Sorby. They have been met with by the author but once in 
the United States. In a sand supply used in Atlanta, Ga., some 
years ago, there could be detected with a glass quite a large pro- 
portion of well-shaped quartz crystals some of which were twins. 
Fig. 2, No. 6, shows the irregular weathered crystals forming this 
sand. 

Such sands are undesirable for an asphalt surface mixture for 
reasons too obvious to require mention. 

Oval Grains are worn much more smooth by continued water, 



THE MINERAL AGGREGATE. 57 

tidal or glacial action, the original angles being mostly or entirely 
lost. Tidal action has a peculiar tendency to produce grains with 
one diameter longer than the other, as particles with this peculiarity 
arrange themselves with their longer diameter in the direction of 
the force of the waves and are then worn still more into this shape. 
Seabeach sands are supposed on this account to be far from sharp, 
but that on the Florida beaches is markedly so. Fig. 2, No. 1. 

Round Grains.— Round-grained sands are not uncommon. They 
are oftener found in river, glacial, and seolian sands, which are 
worn by being rolled over and over and polished against each 
other like the well-known spheres of quartz prepared by the 
Japanese. Fig. 2, No. 7. It is probable that a very large per- 
centage of sand is composed of the somewhat irregular, rounded 
grains. 

The shape of the grains of a sand has a marked influence, when 
combined with their size and grading, upon the character of the 
asphalt surface mixture made with them, the closeness with which 
they can be packed together depending to a very considerable 
degree on their shape. Round sands and oval sands can be com- 
pressed much more readily than sharp ones, owing to the smaller 
friction between the smooth surfaces, although they may not 
on this account be found to pack as closely eventual] y. Whether 
the shape of the grains in the sands in use in paving mixtures has 
any effect sufficient to account for the cracking of some surfaces 
more than others is a question for investigation. It may so 
influence the character of the voids in a mineral aggregate as to 
do so. This will be considered later. Mixtures made with round- 
grained sands are of course less stable and mark more easily in 
summer than those made with sharp sand, since round particles 
move much more readily over one another than sharp ones ; but, 
on the other hand, with plenty of filler this tendency can be neu- 
tralized, while the round-grained sands can be packed much more 
readily and closely and with smaller voids and the resulting sur- 
face can, in this way, be made denser. 

Surface of Sand.— The character of the surfaces of sand grains 
is very different, much more so than would appear from mere 
ocular examination. Under the microscope sand grains are found, 



58 THE MODERN ASPHALT PAVEMENT. 

as shown in our classifications, with the surfaces of the original 
material of which the grains are composed, or with the surfaces 
derived from fracture of this material. There are surfaces polished 
by attrition and water action, surfaces like ground glass, Fig. 2, 
No. 7, originating in the same way, surfaces coated with the 
cementing material originally uniting the grains into a sandstone, 
surfaces acted upon chemically, and the porous surfaces of lime- 
stone and coral grains. The different kinds of surfaces behave 
quite differently toward asphalt cement. The porous limestone 
surfaces absorb it and it, of course, adheres very firmly. To 
the quartz surfaces the bitumen adheres in most cases well, but 
in others only slightly, being readily washed off with water. Some 
quartz grains will carry a heavy coat of asphalt cement, others 
but a small and thin one, as can be detected by examining with 
a glass mixtures made with different sands. 

These peculiarities can be explained by the difference in the 
capacity of surfaces of different character for retaining or adsorb- 
ing bitumen, the film adhering being thicker in one case than in 
another. They have a very decided effect upon the character 
of different mixtures and may well be the cause of cracking in 
surfaces made with certain kinds of sand. As has been already 
remarked, a sand from the London gravels has a surface such that 
asphalt cement would not adhere to it in the presence of the damp- 
ness of a London fog, so that it would be found in the gutters 
after a rain, washed quite clean and free from bitumen. 

That even water has strong chemical effect on the surface of 
sands, thus altering its character, can be seen from Daubree's 
experiments already alluded to. Geikie quotes him as follows: 

"Daubree endeavored to illustrate the chemical action of 
rivers upon their transported pebbles by exposing angular frag- 
ments of feldspar to prolonged friction in revolving cylinders of 
sandstone containing distilled water. He found that they under- 
went considerable decomposition, as shown by the presence of 
silicate of potash, rendering the water alkaline. Three kilograms 
of feldspar fragments made to revolve in an iron cylinder for a 
period of 192 hours, which was equal to a journey of 460 kilo- 
meters (287 miles), yielded 2.720 kilograms of mud, while the 



THE MINERAL AGGREGATE. 59 

5 litres of water in which they were kept moving contained 12.60 
grams of potash, or 2.52 grams per litre." 

Of course quartz grains are not attacked like the feldspar, 
and it is for this reason that in sands resulting from the decomposi- 
tion of rocks containing feldspar none of the latter remains and 
the grains of which it is composed are all quartz, hornblende, etc. 

From what has been said in the preceding paragraphs the very 
variable character of sand, apart from the size of the grain, will 
be readily understood. All of these characteristics demand care- 
ful consideration in the selection of sands for successful asphalt 
surface mixtures. But more important even than these considera- 
tions is the size of the grains which go to make up any sand. 

Size of Sand Grains. — The size of the sand grains in an asphalt 
pavement, that is to say their average diameter, is of the greatest 
importance, as will be found in studying the subject of surface 
mixtures. Sands occur in nature in which are found every size 
grain from the impalpably fine quartz of silt to fine gravel. In a 
standard sheet asphalt surface it has been found generally prefer- 
able to have no sand grains larger than 2 millimeters in diameter, 
passing a 10-mesh sieve made of wire .027" in diameter, or smaller 
than .17 millimeter, which pass a sieve of 100 meshes to the inch, 
made of wire .0043" in diameter. It is always possible to exclude 
the coarser grains, but it is not so easy to get rid of the material 
which is too fine. 

Sands are differentiated into various sizes by means <Df sieves 
somewhat arbitrarily made, but so selected for use in the asphalt 
industry that the average diameter of the particles shall bear a 
definite relation to each other. The finest sieve in use, 200 meshes 
to the inch, made of wire .00235" in diameter, passes particles of 
all degrees of fineness up to a diameter of .10 to .083 millimeter. 
The coarsest particles passed by this sieve are plainly sand and are 
generally round and usually undesirable. The next sieve in 
use has 100 meshes to the lineal inch and is made of wire .0043" 
in diameter. It passes particles having a diameter of about 
.17 millimeter, or double that of those passing the 200-mesh sieve. 
The next, made of wire .00575" with 80 meshes, passes particles 
of a diameter of .23 to .24 millimeter, three times that of the 200; 



60 



THE MODERN ASPHALT PAVEMENT. 



the next, made of wire .0090" in diameter, 50 meshes, particles 
of about .37 millimeter, or four times the finest sieve. The 40- 
mesh sieve, made of wire . 01025", however, passes at a jump to a 
particle six times the diameter; the 30, made of wire .01375" 
in diameter, to one of eight times; the 20, made of wire .01650" 
in diameter, to one of about twelve, and the 10, made of wire 
.027" in diameter, to one of about twenty to twenty-five times 
the diameter of the largest grain passing the finest sieve. A more 
minute differentiation than this of the size of the sand grains 
would be burdensome and of no advantage. For this reason 
sieves of 150, 90, 70, and 60 meshes to the inch are not used in the 
paving industry. As an example of the use of these sieves the 
great difference between the size of the particles of a sand suitable 
for hydraulic concrete and that suitable for an asphalt surface 
mixture will serve and is seen to be quite marked. In the former 
a coarse sand is sought, in the latter a fine one. 



Hydraulic 
Concrete Sand. 



Paving Sand. 



ssing 200-mesh 
" 100- " 
" 80- " 


sieve. 
it 


" 50- " 


tt 


" 40- " 


tt 


30- " 

" 20- " 

10- " 


It 
It 
a 



Trace 

1% 

2 
17 
18 
24 
22 
16 

100 



17% 

17 

30 

13 

10 



100 



It will be observed in the above sittings that the results are 
stated in percentages of the material passing the various sieves. 
This method of statement is much to be preferred to that in which 
the percentages remaining on the different sieves are given, and for 
two reasons. In the first place it enables one to judge of the 
size of the grains from the diameter of the meshes and the size 
of the particles passed by such a mesh, which cannot be done 
from the percentage remaining on the sieve. In the second 
place, as will appear from the description of the method of making 
a sifting in Chapter XXVIII, it is much more easy to remove the 



THE MINERAL AGGREGATE. 



61 



fine material which passes the 200-mesh sieve by attrition of the 
coarser grains one upon another and upon the cloth of the sieve 
than to separate out the coarser grains first and afterwards weigh 
the remaining 200-mesh material, especially as there is apt to 
be a loss of this material during the process of sieving, which 
makes no difference if it is sifted out first and the amount deter- 
mined by loss. 

The sieves which are used for the sifting are carefully made in 
large lots by one firm from the same lot or roll of cloth woven 
for the purpose, so that several sets shall be so nearly alike as to 
give uniform results even in different hands. 

COMPARISON OF THE SIEVING OF TWO SAMPLES OF SAND 
ON DIFFERENT SETS OF SIEVES IN DIFFERENT LABO- 
RATORIES. 



Sample number. 
Sittings 



Passing 200-mesh sieve. 
100- 
80- 
" 50- 
" 40- 
" 30- 
*' 20- 
" 10- 



Lab. No. 1 Lab. No. 2 



15% 
25 
12 
28 

8 

5 

5 

2 

100 



15% 

25 

12 

26 

11 

5 

5 

1 

100 



Lab. No. 1 Lab. No. 2 



10% 

15 

17 

33 

10 

5 

6 

4 

100 



10.5% 

18.9 

10.5 

34.7 

11.5 

6.3 

3.2 

3.1 

98.7 



While the agreement in the siftings obtained with sieves made 
in this way is as concordant as could be expected a similar agree- 
ment will not be found among sieves obtained from different 
sources, especially in the case of the finer ones with 80, 100, and 
200 meshes to the linear inch. In explanation of the difference 
in the character of the cloth woven by the different manufacturers 
Messrs. Howard & Morse, of Brooklyn, N. Y., who manufacture 
the sieves in use by the author, have the following to say in reply 
to certain questions which were propounded to them. 

In reply to the inquiry as to where the cloths in use for making 
these sieves are manufactured they state that: 



62 THE MODERN ASPHALT PAVEMENT. 

"Wire cloth of iron, steel, brass, or copper, from the coarsesl 
to No. 100 mesh, is made in this country, while the finer meshes 
are imported from France, Germany, and Scotland. We think 
the Scotch cloth is the best. Even 100 mesh can be imported at 
a lower cost than the rate paid our weavers will allow it to be 
produced. . . . We do not believe any American manufacturer could 
be induced to make the necessary outlay to produce cloth finer 
than 120, unless the field for its usefulness was very much enlarged, 
as the imported cloth at a much lower cost seems to answer every 
general purpose for which such cloth is used. Moreover it might 
be necessary to import the workmen/ 7 

As regards the process of manufacture they say: 

"Beginning with wire, say, ^" in diameter, the mill draws 
down to smaller sizes until too hard to safely draw smaller; it 
is then annealed, when, its ductility being restored, it is drawn 
down finer, and then reannealed, and the process repeated until 
the requisite size is obtained and it is given its final annealing, 
to render it fit for fabrication into cloth. The wire is delivered 
by the mill to the wire-cloth manufacturers in skeins, which are 
rewound on spools according to the mesh required. Usually the 
process is as follows: 

"Take for instance 100 mesh. We desire to put on a 'warp' 
say 36"x300 feet. This will make 3 ' cuts' each 100 feet long. 
We estimate the weight, allowing for waste and 'thrums,' and 
taking a little over one-half the total weight, we divide this as 
equally as we may among the 100 spools, being careful that none 
are under weight. The spools are placed in a rack as closely as 
convenient; the wires from each spool are led through a device 
which prevents their crossing (and serves other purposes of a 
nature somewhat complicated to explain) to the ' back-beam of 
loom.' The 100 wires are what we term an inch. They are 
tied together at the end and hook over a bolt-head in a slot which 
runs lengthwise of the beam, which in our looms is about 5' 
circumference and 52" long. For 36" width we hook our first 
inch on peg 18" from centre. For 300 feet we would need to put on 
60 'rounds,' i.e., the beam (which is really a heavy hollow cylinder) 
is turned 60 times, and the ' lease ' wire separating the contigu- 



THE MINERAL AGGREGATE. 63 

ous wires alternately above and below is put in place and the 
beam turned up one more revolution to allow for distance from 
back-beam to face of loom. 

"The inch is then secured to another peg, which is firmly 
secured in the partition between the inches, these partitions form- 
ing 'grooves ' in which the wires lay, and the bunch of 100 wires 
is then cut off and the second groove receives its 60 rounds, and so 
continued till the 36 grooves or inches are filled. This is a slow, 
tedious process. 

"However careful may be the windings of the spools, whatever 
device may be used for spool racks, yet the wire will catch and 
break, and it is necessary to repair every break before another 
round is turned up on the back-beam. If the spools run too freely, 
the wire comes off too fast, and a ' bight ' will draw into a kink 
and snap even with comparatively heavy wires, or the bight will lay 
across other wires and catching may snap a dozen or more. How- 
ever, the warp being on the back-beam, one inch is taken off the 
peg, and the wires, being separated by the ' lease/ are passed each 
one in the order in which it lies in the grooves, first through the 
'gears,' or 'heddles/ and next through the 'reed.' The heddles 
consist of two frames about 8 to 10 inches high by the width of 
the loom in length, secured in a variety of ways; to these frames 
are attached twisted wires with an eye in the centre. For 100 mesh 
each frame must contain at least 50 of these twisted wires to each 
mesh. The 100 wires we have loosed from the back-beam are passed 
in their exact order alternately through back and front gear, or 
rather 50 are passed through the eyes of the back-gear and the other 
50 passed between the wires of the back-gear through the eyes of 
the front. 

"These gears being operated by treadles, it is evident that 
when the back-gear is down and the front one is up from the normal 
line in which wires would tend to lie, that a ' shade, ' or shed, is 
formed, every alternate wire being in the upper, while the others 
are in the lower shade, or shed. The shade at the gears may be 
3", while at the face of the cloth it is nil, and in front of the reed 
when swung back as far as the lay will carry it may be 2" '. The 
lay, or ' beater, ' is hung overhead and is provided with a groove 



64 THE MODERN ASPHALT PAVEMENT. 

in what is known as the bottom shell, and also in the top shell, 
which is removable and adjustable vertically to suit reeds of various 
heights, which are so placed in the shells as to have free lateral 
play, but very little in any other direction. All the inches being 
successively passed through the gears and reed, they are properly 
fastened to a ' sacking ' which leads from the face of the reed around 
a ' breast-beam ' down to the ' cloth-beam/ on which it is wound up 
as the cloth is made. 

"The reed consists of a series of ' splits ' made of flat steel of pecul- 
iar temper. In a 100-mesh reed they would probably be about 
&" wide, and the thickness of each split would be equal to a trifle 
less than the space between the wires of the cloth. They are 
compacted into reeds by a process of lacing, which must be very 
particularly done, as the split must stand square to plane of cloth, 
parallel, and evenly spaced, the spaces being a trifle more than the 
thickness of the wire which passes through them and there must 
be exactly 100 in each and every inch. The warp being already 
to commence weaving, the weaver, stepping on the treadle, opens 
his shade and throws his shuttle through, catching it on the other 
side of the piece, the lay is brought up one blow and he changes 
his treadle and gives a second blow to place the shot. After throw- 
ing 100 shots and giving 200 blows he has completed 1 inch, when 
he proceeds to count it and thus discover whether he is driving the 
1 woof, ' or ' filling, ' up too hard or too lightly to place 100 trans- 
verse wires in 1 inch. 

"Until fairly started his warp-wires will be constantly break- 
ing in fine cloth, and it is a constant contest of patience, with 
unavoidable delays, until the last shot is thrown, though always 
worse at the beginning and gradually diminishing. After 2 or 3 
inches have been made the weaver gets the ' blow ' necessary to secure 
the required fineness in the mesh, and many become very expert and 
exact; that is, we thought it was exact until Mr. Richardson called 
our attention to many inaccuracies and defects. Being as good 
(perhaps better) than similar work from other factories, it sold 
and we heard no complaint of inequalities until this cement testing 
question brought us face to face with a different problem." 

The size of the wire with which any cloth is made will of course 



THE MINERAL AGGREGATE. 



65 



have a decided influence on the width of the meshes of the cloth 
for any given number per lineal inch. Messrs. Howard & Morse 
state that while cloth of the same mesh can be made of many 
different sizes of wire, as shown for the coarser sieves by the ordinary 
trade catalogues, the difference is more theoretical than practical 
when we go beyond the 60- or 70-mesh sieves. For the four finer 
sieves in use in the asphalt-paving industry the diameter of the 
wire, the mesh, and the space between the meshes are intended to 
be as follows: 



Mesh. 


Mesh. 


Diam. of 
Wire. 


Space. 


No. 50 No. 35 0. E. gauge wire. . . 
" 80 " 38 " " " ... 
" 100 " 40 " " " ... 
" 200 " 42£B. &S. wire 


.02 
.0125 
.01 
.005 


.009 
.00575 
.0043 
.00235 


.011 
.00675 
.0055 
.00265 



In reply to the question as to why the ordinary cloth is much 
more regular in the number of meshes to the inch in the one direc- 
tion than it is in the other the makers of the sieves say: 

"If the reed be exact the cloth must have the proper number 
of holes one way, as it is governed by the reed. The reason that 
cloth sometimes has fewer holes the other way is that it is governed 
by the blow given by the weaver. If he can pass coarse cloth 
under the eye of the inspector, he gains the few missing shots in 
each inch and the same number of blows may in a day's work gain 
him 5 to 10 per cent more pay, but it is not so often the intention 
of the weaver so to deceive. A warp of 100 may be put on the loom 
in December and not be out until the following June. It is slow 
work. Consider the effects of various temperatures and other 
causes which may affect a man's disposition meanwhile. Too gay 
or cheerful, you would be obliged to check his blow which would 
drive cloth too fine. In brisk, cool weather cloth would be driven 
up finer than in warm, uncomfortable weather. Again, a fresh 
start in the morning means better cloth than that made in the 
later hours of the day. We have been accustomed to pass a coarse- 
ness not exceeding 5 per cent; i.e., we would accept 80X76 as a 
square mesh. Again, the wire is not even in either temper or sifce. 



66 THE MODERN ASPHALT PAVEMENT. 

Hard wire or wire a trifle larger than it should be will not 'go 
to place' with the same blow that soft, proper gauge wire would 
require. We select all wire as carefully as possible, and though 
a great difference is not common in a single skein, yet the writer 
has gauged a skein of brass wire which has shown a full size dif- 
ference when gauged at both ends. Not being wire-drawers, we are 
at a loss to account for this. It seems almost impossible that a 
die should be worn so perceptibly in drawing less than a mile of 
wire, and yet one end of the skein may be round while the other 
is elliptical in cross-section. These causes and others all tend 
to an irregularity of mesh which shows that the weaver is not 
entirely at fault. 

" To eliminate any question of nicety of touch and skill on the 
part of the weaver, fortunes have been sunk in experiments to pro- 
duce an automatic loom; but the other causes remain, and though 
they affect the accuracy to a less degree in a power loom, yet 
they have a strong influence. We have power looms that will 
make the cloth exact, but cannot use them for anything finer than 
20 or 30 mesh, and with only a medium- weight wire. Another cause 
that may affect the mesh is the inequality of 'temper/ or in 
other words, speaking of other metal than steel, we should per- 
haps say, 'malleability/ hardness, or softness, but we have come 
to use the word 'temper/ however incorrect it may be, in reference 
to all metals used in fabrication of wire cloth. 

"The degree of heat to which wire is subjected in the anneal- 
ing process may vary with the different charges; more than 
this, it may vary with the heat applied to the different skeins in 
a single charge, and more troublesome still, it may be hotter on 
one side of the skein than on the other. This makes serious in- 
equalities in the 'temper' and in consequence a variation in the 
mesh of the cloth in which it is to be used." 

Messrs. Howard & Morse also add as a reason for the great 
variability in the sieves offered by the trade: 

"That each wire-cloth manufacturer has ideas of his ^wn 
as to what the trade requires; for instance, he may use 48 reed 
for 50 mesh and have his cloth driven up to 44 the other way, 
so that he will furnish you on your call for 50 mesh a piece 48X44, 



THE MINERAL AGGREGATE. 67 

while the manufacturer who gave you 50X50 on your call gives 
you a cloth that costs him more, both for material and labor than 
the other. 

" Again, certain trades, notably the paper trade, requires cloth 
not driven up square, and 48X38 passes for 50 mesh, 68x52 for 
70 mesh, and if this cloth passes through other channels, as a dealer's 
hands, he will sell a piece to am^ transient customer, say 58X46, 
and call it 60 mesh, and with entire innocence, for he bought it for 
60 mesh. 

"Mill strainer cloth is another irregularity. It is made of 
very light wire and not driven up with any approach to accu- 
racy. In fact the low price obtained for it prohibits care in its 
manufacture. It is either woven by boys or on a power loom, 
which, as explained above, will not insure accuracy in fine meshes." 

The Committee on Uniform Tests of Portland Cement of 
the American Society of Civil Engineers at one time hoped that 
all sieves in use in the testing of cement might be constructed 
of wire the diameter of which should be one-half the width of the 
opening. If sieves could be constructed on this plan it would 
no doubt be very desirable, but in response to an inquiry as to 
whether this could be done the manufacturers make the following 
statement : 

"To make fine brass cloth with the diameter of wire one-half 
the width of opening would result in a flimsy fabrication which in 
use would give you more unsatisfactory results than you now 
attain. 

"The individual wires would be of very little use and not only 
break very easily, but would push to one side or the other; two con- 
tiguous wires crowding each the neighboring wire would separate 
and give space four times the size natural to the mesh. We find 
that in order to make a fairly rigid cloth it is necessary that the 
diameter of wire be about 80 per cent of space size, or practically 
as shown in table on page 65. To make the lighter wire would 
increase cost, though we presume that is of minor importance, and 
yet it must be considered. It would be difficult to make this per- 
fectly clear perhaps. To take a sample case of frequent occur- 
rence: Our customers know that in the coarse grades of cloth 



68 THE MODERN ASPHALT PAVEMENT. 

for a certain mesh the price diminishes as diameter of wire 
decreases, and this is true up to about 60 mesh. We make this 
from stock of No. 36 O. E. gauge wire (.0075"). They order No. 37 
in hope of obtaining it at a lower price per square foot. The 
weight of 60 of No. 37 is 75^ per cent as great as the weight of 60 of 
36 ; and yet material for 37 costs about 40 per cent more per pound 
than 36. This difference becomes greater as we advance to the 
finer sizes. No. 200 mesh is made of .00235" wire (as near as the 
micrometer gauge will show it). The finest wire the writer ever 
saw was silver .002" in diameter, and this w r as shown as a curiosity 
rather than of any practical use. 

"It may be that the ductility of brass is sufficient to make 
it practicable to draw it to .0017", but we doubt it, and at 
what expense? 105,263' to one pound, i.e., to draw one pound 
.0017" brass wire about 20 miles of wire must pass through the 
dies. This is getting down to fine work. It means about sixteen 
days' work to one pound, and the finer the wire the more slowly 
it must be drawn. We do not mean weight, for that is evident, 
but as regards length. Imagine, too, the making of the die. Can 
one expect it to be round, square, or true to any regular shape, 
or exactly accurate with regard to size? 

"Take even our 80 mesh, the wire wherein is .00575" in diame- 
ter, nearly 3^ times the diameter of the wire you specify for the 
200 mesh, 11^ times as large in area of cross-section, consequently 
11^ times as heavy in a given length, and contemplate the skill 
required to make a hole in a die which shall be round and with 
an exact diameter smaller than the hole in 100-mesh cloth. Con- 
sider the care necessary in drawing this wire, constant watching 
to note when the die is worn too large, and the whole manipulation 
until wire is woven into cloth and put into sieves, and there will 
be apparent reasons sufficient for the inaccuracies noted by you 
from time to time. 

"Up to 100 mesh we can make a cloth as accurate as any one 
in the trade; beyond that we cannot control it. We will write 
parties in Glasgow in a few days, and if we can learn any- 
thing of interest to you will be glad to communicate it to 
you. 



THE MINERAL AGGREGATE. 69 

" We are willing to put on a short warp, say 36"X 100 feet each 
Nos. 50, 80 and 100 mesh, guaranteeing that it shall be driven 
up square, i.e., the 50 to between 48 and 50, and the 80 between 
77 and 80, and the 100 to between 97 and 101, the wire carefully 
selected to conform to size given in answer to No. 5 (see table, 
on page 65), within 2 per cent of diameter, provided you will 
agree to find sale for same, at list price net, within one year of 
completion. 

"We are aware that we are undertaking a hard piece of work. 
The delays will be expensive; we shall expect to pay more than 
the usual price for the wire; every skein will need to be gauged 
at both ends, and if long, in the centre as well; much of the wire 
will have to be discarded; the mill contests our claims of inaccuracy; 
the cloth will have to be carefully and constantly watched, and 
the supervision will be onerous, but we are desirous of giving 
you all the satisfaction possible, though naturally without pecuniary 
loss to ourselves, and we therefore do not consider the whole 
cost of supervision in naming the above price." 

The preceding explanation will enable the reader to grasp the 
difficulty of obtaining satisfactory sieves more readily than any- 
thing that could be said by the author, and it will show the care 
which is used in order to obtain, for use in the asphalt industry, 
sieves which are at least uniform among themselves and which 
can be considered as standards, at least arbitrarily if not abso- 
lutely. 

That a better grade of 200-mesh cloth can be obtained which 
is much more regular than the average supply can be seen from 
the accompanying illustration, Fig. 3, where the good can be dis- 
tinguished from the poor cloth without difficulty, and where it 
can be seen that the lack of regularity is due to the manner in 
which the weaver pushes up the wire. 

Until 1907, the 200-mesh cloth was twilled, but since that 
time Messrs. Howard & Morse have produced a plain woven cloth, 
which in some ways is more satisfactory as far as the number of 
mashes per inch is concerned, but will probably not wear as well 
as the twilled material. Three counts of this cloth recently made, 
resulted as follows : 



70 THE MODERN ASPHALT PAVEMENT. 

Warp. Woof. 

First piece 200 197 

Second piece 200 197 

Third piece 200 198 

while the 100-mesh cloth made at the same time with great care 
counted 

Warp. Woof 

First piece 100 98 

Second piece 100 102 

These counts are much more satisfactory than those which 
were formerly obtained. 




Good Cloth. Poor Cloth. 

Fig. 3. 

The sieves are generally known, as has appeared in what has 
been said, by the number of meshes which they show to the linear 
inch. For strictly scientific purposes they would be more properly 
identified by the diameter of the largest particle which each sieve 
would pass, and these diameters have already been given for the 
sieves which are in use in the asphalt industry. For the purpose 
of determining this diameter Mr. Allen Hazen adopted a method 
which he describes as follows: 1 



twenty-fourth Annual Report cf the State Eoard of Health of Mas- 
sachusetts, 1892, 541. 






THE MINERAL AGGREGATE. 71 

"It can be easily shown by experiment that when a mixed 
sand is shaken upon a sieve the smallest particles pass first, and 
as the shaking is continued larger and larger particles pass, until 
the limit is reached, when almost nothing will pass. The last and 
largest particles passing are collected and measured, and they 
represent the separation of that sieve. The size of separation of 
a sieve bears a tolerably definite relation to the size of the mesh, 
but the relation is not to be depended upon, owing to the irregu- 
larities in the meshes and also to the fact that the finer sieves 
are woven on a different pattern from the coarser ones, and the 
particles passing the finer sieves are somewhat larger in proportion 
to the mesh than is the case with the coarser sieves. For these 
reasons the sizes of the sand grains are determined by actual 
measurements regardless of the size of the mesh of the sieve. . . . 

"The sizes of the sand grains can be determined in either of 
two ways: from the weight of the particles or from micrometer 
measurements. For convenience the size of each particle is con- 
sidered to be the diameter of a sphere of equal volume When 
the weight and specific gravity of a particle are known, the diameter 
can be readily calculated. The volume of a sphere is %nd 3 , and 
is also equal to the weight divided by the specific gravity. With 
the Lawrence materials, the specific gravity is uniformly 2.65 
within very narrow- limits, and we have 



2^5 = ^ 3 - 



Solving for d we obtain the formulae 

when d is the diameter of a particle in millimeters and w its weight 
in milligrams. As the average weight of particles when not too 
small can be determined with precision, this method is very accu- 
rate, and altogether the most satisfactory for particles above 
.10 millimeter; that is, for all sieve separations. For the finer 



72 THE MODERN ASPHALT PAVEMENT. 

particles the method is inapplicable, on recount of the vast num- 
ber of particles to be counted in the smallest portion which can 
be accurately weighed, and in these cases the sizes are determined 
by micrometer measurements. As the sand grains are not spher- 
ical or even regular in shape, considerable care is required to ascer- 
tain the true mean diameter. The most accurate method is to 
measure the long diameter and the middle diameter at right angles 
to it, as seen by a microscope. The short diameter is obtained 
by a micrometer screw, focusing first upon the glass upon which 
the particle rests and then upon the highest point to be found. 
The mean diameter is then the cube root of the product of the three 
observed diameters. The middle diameter is usually about equal 
to the mean diameter, and can generally be used for it> avoiding 
the troublesome measurement of the short diameters. 

"The sizes of the separations of the sieves are always deter- 
mined from the very last sand which passes through in the course 
of an analysis, and the results so obtained are quite accurate." 

Voids in Sand. — Sand consists of particles of such shapes that 
they cannot be packed in any space without leaving intervals 
between the grains which are not filled. These spaces are known 
as voids and their volume and the size of the spaces are very impor- 
tant in characterizing different sands. The amount of volume 
of the voids and their size are dependent on the "Shape and variety 
in the size of the grains, upon the way they are arranged, and upon 
the degree to which they are compacted. If the sand grains were 
perfect spheres it can be regularly calculated what the percentage 
of voids in any volume will be. Dr. G. F. Becker, of the United 
States Geological Survey, has made this calculation for me and 
states the results as follows: 

"Suppose, first, that 8 spheres of radius r are so arranged that 
the centre of each is at one corner of a cube and that the edge 
of the cube is 2r. Then one-eighth of each sphere will be included 
within the cube, and the total of the spherical matter in the cube 
will be just one sphere. In this case the voids will be 

SMJHS!.! « . 4764 . 

(2r) 3 6 



THE MINERAL AGGREGATE. 



73 



"Now shift the four spheres forming the lower layer into this 
order 




which amounts to changing the angles made by the edges of the 
cube without any change in length. Also bring the centres of 
the upper layer of spheres over the point marked "x". Then 
the cube is distorted into an oblique prism of which this is a plan. 




"It still includes just one sphere. The area of the lower sur- 
face of the prism will be 




74 THE MODERN ASPHALT PAVEMENT. 

2r^ = 2r.2rsin60° 

= 2rV3 

and the height of the prism is the height of a tetrahedron formed 
by the centres of four spheres when three are placed in contact 
in one plane and the fourth is laid upon them. This height, and 
thus the whole volume of the prism, is 



2r 2 V3".rJ|=4V2r3 



and the interstitial space is 
4v / 2r3-f 7 rr3 



4V2r 3 3V2 



=0.2595 



"By diminishing all lines in one direction in the same propor- 
tion the system of spheres becomes a system of ellipsoids. Since 
the spheres and the interstitial spaces are distorted in the same 
manner, it is evident that a system of equal and similarly oriented 
ellipsoids may also be packed so as to leave only 25.95 per cent 
of voids. But if any ellipsoid is differently oriented from the rest, 
the voids will be greater." 

With the spheres or regularly oriented ellipsoids packed as 
closely as possible the voids should therefore be 25.95 per cent, 
but it is not possible to pack small grains like sand in this regular 
way. They are jumbled together irregularly, and experiment has 
shown that perfect spheres like small bird shot when shaken 
and tamped until they are as compact as it is practical to make 
them with the devices at our command still contain voids of 32 per 
cent, or 6 per cent more than theory. 

With spheres of quartz of similar size it would probably be 
impossible to compact them to the same extent, while if the material 
is merely poured loosely into the space which is to be filled and no 
attempt is made to attain greater compaction the voids will be 
found to be very much larger. 



THE MINERAL AGGREGATE. 75 

It is important therefore before going further to consider the 
conditions under which determinations of voids are usually made 
and to decide upon a uniform method, one which is the best to 
use in obtaining results of both absolute and relative value. There 
are several difficulties to be met with in arriving at the ultimate 
practical compaction of sand aside from the impossibility of bring- 
ing small particles of any size and shape into the closest possible 
juxtaposition. 

Determination of the Voids in Sand. — The usual method of 
determining voids in sand, gravel, stone, etc., is to fill a vessel 
of known volume with the material in the condition under which 
it is desired to find the voids and then to pour in water until the 
space between the grains is filled, thus determining the voids 
from the relation of the volume of water to the volume occupied 
by the material examined. This method is satisfactory with 
coarse substances like gravel, but not when grains smaller than 
those which will pass a 30-mesh sieve are present. One reason 
why it is not satisfactory with fine material is because air is liable 
to be entangled between the grains and not to be replaced by 
water. According to another method a definite volume of the 
compacted material is poured into a measured volume of water. 
The increase in volume is that of the material and the difference is 
that of the voids. This is a more satisfactory way if no fine material 
or dust is present, which has a tendency to float in water or to 
obscure the meniscus. 

It is better, therefore, to determine the specific gravity of the 
material of which the grains are composed and then calculate 
the voids from the weight of a definite volume of sand. For 
instance, if 100 cubic centimeters of quartz sand weighs 168 
grammes and the specific gravity of the grains is 2.65 the voids 
may be found by dividing the weight by the gravity multiplied 
by 100 and subtracting the results from 100, the result in this case 
being 100—168-^2.65 = 36.6 which is the per cent of voids by vol- 
ume in this sarid. 

Where the ultimate practical compaction of fine material is 
sought, some further precautions must be taken, as this cannot be 
accomplished at all at ordinary room temperatures, as a film o{ 



76 



THE MODERN ASPHALT PAVEMENT. 



adsorbed aqueous vapor adheres to each grain, which keeps them 
apart. With dust or 200-mesh material alone, air also is often 
imprisoned in the mass and increases the voids. If, however, the 
sand or dust is heated above the temperature of boiling water these 
difficulties are removed and the fine grains compact as well as 
coarser ones. As examples, the voids found in a sand and in a 
ground limestone when determined with hot and cold materials 
respectively were : 

VOLUME OF VOIDS. 





Cold. 


Hot. 


Sand 


34.2 
56.6 


33.3 
38.0 


Dust. 





In each determination the means employed for compaction 
were the same, but only when the material was hot was this com- 
plete, especially with the fine dust. The degree of compaction to 
which a substance such as sand is subjected of course influences 
the extent of the voids. The relation between those in a mass 
loosely poured into a cylinder and slightly shaken down but 
not compacted and those in a thoroughly compacted mass can 
be seen from the following determinations: 

VOIDS. 




Thoroughly 
Compacted. 



Long Island sand — coarse. 

Buffalo — fine. . 

Chicago 

New Orleans — very coarse 
Kansas City — very fine. . 



33.7 
37.9 
35.5 
29.6 
36.0 



The voids in sands and mineral aggregates should of course 
be determined in a state of thorough compaction, as this is the 
condition in which these materials are or should be found in a 
finished asphalt surface. 



THE MINERAL AGGREGATE. 



77 



Weight per Cubic Foot. — The voids being known in any sand 
or aggregate, and the gravity of the particles (for all practical 
purposes for quartz sand this may be taken as 2.65), the weight 
per cubic foot is calculated and is usually stated together with 
per cent of voids, as it is a factor of some importance in consider- 
ing the relations of bitumen to the aggregate in certain surface 
mixtures, sand being frequently taken by volume — 9 cubic feet — 
and as an indication of possible density of the finished surface. 

The very considerable variations in the voids and weight per 
cubic foot in various unmixed sands examined in 1894 and later 
are seen in the following tables, pages 77 and 78. 

VOLUME WEIGHTS AND VOIDS IN SANDS. 



Wt per 
Cu. Ft. 
Loose. 


Voids. 


Wt. per 

Cu. Ft. 

Compact. 


92.0 


45.4 


102.7 


97.1 


41.2 


110.4 


103.4 


37.6 


116.4 


100.9 


39.1 


113.6 


95.1 


42.5 


109.1 


82.4 


51.2 


95.3 


98.6 


40.4 


109.1 


94.9 


42.6 


107.8 


86.6 


44.9 


99.9 


94.6 


42.8 


106.6 


92.9 


43.8 


106.5 


95.6 


42.2 


107.7 


94.0 


43.3 


106.4 


94.4 


43.0 


108.3 


87.0 


46.9 


105.9 


101.7 


38.5 


112.9 


92.4 


44.1 


105.1 


92.4 


44.1 


105.0 


92.1 


44.3 


107.6 


89.4 


46.0 


99.8 


91.9 


44.5 


101.6 


91.4 


44.7 


108.8 


89.2 


46.1 


100. 1 


£3.4 





97.0 



Voids. 



Ballast — very fine 

Buffalo— No. 3 

New Orleans — Prophet Island — coarse. . . 
' ' screened 

' ' — lakeshore 

' ' — Jordan River — much loam 

Omaha 

London — coarse 

" —fine 

Yonkers — coarse 

" —fine 

Chicago 

Boston 

New York 

Kansas City — fine 

' ' — coarse 

Altoona 

Youngstown 

Niagara Falls — No. 1 

" — " 2 

Louisville 

Fort Wayne 

AYashington 

Harrisburg — (much coal) 



37.9 

33.2 
29.6 
33.3 
34.0 
42.4 
34.1 
34.8 
39.6 
35.6 
35.6 
35.0 
35.7 
34.6 
36.0 
31.7 
37.7 
36.5 
35.0 
40.0 
38.6 
34.3 
39.5 
41.3 



Voids as Affected by Size and Shape of Particles and by their 
Uniformity. — With the method of determining the voids in sands 
in a uniform and satisfactory way in mind, the peculiarities found 
in the aggregation of particles of mineral matter of different shape 
and size may be considered. 

Voids in Sand Consisting of Particles of Uniform Size. — If the 



78 



THE MODERN ASPHALT PAVEMENT 



particles of a sand are all of uniform size, or nearly so, the voids 
present under our normal conditions will depend upon the shape 
of the particles alone. Sand the grains of which are perfect 
spheres would have, as has been noted for fine shot, voids of 
32 per cent, theory being 25.95, whereas irregular fragments, 
such as are found in crushed stone, the crushed quartz of the 
sand-paper manufacturer, contain practically about 44 per cent, 
but if the particles are uniform their absolute size has no influence 
on the volume of the voids they show. As examples, the following 



GRADING, POUNDS PER CUBIC FOOT, AND VOIDS IN VARIOUS 

SANDS OF 1899. 



Test 
No. 



22693 

22694 

22768 

22769 

22789 

22790 

22802 
22803 
22827 

22917 

22925 

22967 

22968 



Source. 



Paterson, Sand Hill 
No. 16. 

Paterson, Sand Hill 
No. 17 

Scranton, Temper- 
ing No. 1. 

Scranton, Temper- 
ing No. 2 

Louisville No. 1 , 
coarse 

Louisville No. 1, 
fine 

Saginaw, fine bank. 
Sag. River 

La Fayette No. 9, 
Wagner bank. . . . 

Kansas City, Kaw 
River, coarse. . . . 

Washington No. 3, 
crusher dust. .... 

Chicago, fine sand. . 
' ' coarse sand 



Passing Mesh. 



200 



100 



50 



40 



30 20 



10 



Total. 



100% 
100% 
100% 

100% 

100% 

100% 
100% 
100% 

100% 

100% 

100% 
100%, 
100% 



-3 s 



10% 

5% 



Lbs. 

per 

Cu. Ft 



104 
102 
104, 

97. 

99. 

103. 
102. 
107. 

107. 

112. 

105, 

99 

104 



36.6 

38.1 

36.6 

39.6 

39.6 

37.4 
30. 1 
35.1 

35.1 

32.1 

35.8 
39.6 
36.6 



determinations of voids in crushed quartz of uniform but very- 
varied size will sieve: 



THE MINERAL AGGREGATE. 



79 



Crushed Quartz — very Sharp. 


Volume Per 
Cent of 
Voids. 


Passing 6-mesh sieve — not passing 10. . . 
20- " " — " " 30. .. 
90- » " _ " " 100. .. 


43.3 
43.4 
44.2 



These materials represent a very coarse sand, a sand of size 
in use in concrete, and a very fine sand but all of the particles 
of very uniform size. They all contain, when compacted hot, 
the same volume of voids. Without compaction material of 
this description will, however, vary in proportion to the fineness 
of the particles; a coarse broken stone of uniform size will have 
47 per cent of voids, while a similar fine sand will often have over 
50, owing to the fact that the finer material will not naturally 
assume the same degree of compaction as the coarser material. 

The crushed quartz, the voids in which, when compacted, 
have just been given, consists of extremely sharp particles with 
the angles of the original fracture unworn. In sands the grains 
are more or less round as has been shown, and in consequence 
they pack more readily and closely. If sands are taken and sepa- 
rated into portions the particles of each one of which are of nearly 
the same size — that is to say, will pass a certain sieve but be 
retained on one of the next smaller size — and the voids are deter- 
mined for each of these, it will be found that there is a very con- 
siderable variation in the voids for the same sized particles of 
different sands and also for the different sizes, and that with all 
of them the voids are smaller in volume than was the case with 
the sharp particles of crushed quartz. Following are illustrations: 



80 THE MODERN ASPHALT PAVEMENT. 

SIFTING. 



Source 


Passing Mesh. 


Total. 




200 


100 


80 


50 40 


30 


20 


10 




Buffalo — Canada lakeshore 
Omaha— Platte River, 1897 
Chicago — fine lake, 1897. . . 
Detroit — fine lake, 1897 


17 

5 
2 
2 

10 
10 
32 


24 
13 

74 
10 

15 

12 
29 


15 
34 
23 

23 

23 

8 

17 


24 

31 

1 

59 

44 
27 
19 


10 
8 


4 
3 


4 
4 


2 
2 


= 100% 
= 100% 
= 100% 
= 100%. 

= 100% 
= 100% 
= 100% 


4 

6 
15 

1 


2 

1 

12 
1 






Kansas City — fine river, 
1897 


1 

7 
1 


9 


Long Island bank, 1897. . . . 
Buffalo — Attica fine bank. . 



See also tables on pages 81 and 82. 

The crushed quartz of about the 100-mesh size contains 44.2 
per cent of voids. The 100-mesh particles of the fine Attica sand 
showed but 42.9 per cent and the same sized grains of the other 
sands much less, until those from the coarse Buffalo supply con- 
tained but 34.5 per cent. 

Voids in Sand of Varying Sized Particles or Grains. — When the 
grains in a sand vary in size the voids are at once reduced in volume 
by the fitting of the smaller particles into the spaces between the 
larger ones, the voids at the same time becoming smaller in size 
as well as in volume. 



THE MINERAL AGGREGATE. 



81 



VOIDS. 





Loose — Hot. 


Source. 


Entire. 


Passing Mesh. 




200 


100 


80 


50 


Buffalo — Canada lake *. 


40.3% 

35.8 

46.3 

41.1 

41.0 

39.2 


48:6% 

'49 .'8 " 
50.1 
48.0 


41.8% 

43.7 

43.6 

45.8 

45.9 

49.0 

45.7 


38.3% 

42.6 

46.6 

44.0 

44.6 

48.1 

47.5 


42.0% 
42.9 
46 8 


Omaha— Platte River, 1897 

Chicago — fine lake, 1897. 


Detroit — fine lake, 1897 


41 3 


Kansas City — fine river, 1897. „ . . 

Long Island — bank, 1897. . 

Buffalo — Attica, fine bank, 1897. . 


42.9 
47.3 

47.1 











Tamped — Hot. 


Source. 


Entire. 


Passing Mesh. 




200 


100 


80 


50 


Buffalo — Canada lake l 


34.6% 

33.5 

39.2 

35.4 

35.3 

33.0 

32.0 


42.1 
37.7 


34.5% 

38.4 

38.4 

39.6 

40.2 

41.8 

42.9 


32.8% 

37.5 

40.2 

39.1 

40.1 

43.4 

41.3 


36.5% 
37.5 
42 3 


Omaha— Platte River, 1897 

Chicago — fine lake, 1897 


Detroit — fine lake, 1897 


37 5 


Kansas City — fine river, 1897. . . . 

Long Island — bank, 1897 

Buffalo — Attica, fine bank, 1897. . 


38.8 
42.4 
41.4 



1 1.33 per cent magnetite. 

When the various sized particles, the voids in which taken sepa- 
rately are shown in the preceding table, are combined in the pro- 
portions found in nature, the voids are then, with one or two ex- 
ceptions, much reduced. This is conspicuous in the Attica sand, 
which as a whole shows 32 per cent of voids, where its 200 mesh 
has 37.7 per cent and the coarser particles over 40 per cent. 

The greatest reduction will of course occur where there are 
enough fine particles present of a size small enough to fit between 
the larger ones — for instance, dust with sand, sand with gravel, 
and gravel with broken stone. It was found that by adding dust 



82 THE MODERN ASPHALT PAVEMENT. 

VOLUME WEIGHT OF HOT SAND, POUNDS PER CUBIC FOOT. 





Loose — Hot. 


Tamped — Hot. 


Source. 


Entire 


Passing Mesh. 


Entire 


Passing Mesh. 




100 


80 


50 


100 


80 


50 


Buffalo — Canada lake ] . . . . 
Omaha— Platte River, 1897 
Chicago — fine lake, 1897. . . 

Detroit— fine lake, 1897 

Kansas City — fine river, 

1897 

Long Island — bank, 1897. . 
Buffalo — Attica, fine bank, 

1897 


98.5 

93.5 
97.2 

97.4 
100.3 

99.4 


96.0 
92.9 
93.1 
89.5 

89.3 
84.2 

89.6 


101.8 
94.6 
88.1 
92.5 

91.5 

85.5 

86.7 


95.6 
94.2 

87.8 
96.9 

94.3 
87.0 

87.3 


108.0 
109.7 
100.3 
106.6 

106.8 
110.8 

112.2 


108.2 

101.6 

101.6 

99.7 

98.7 
96.1 

94.2 


110.9 104.8 

103.1103.1 

96.7 95.3 

100.6103.2 

99 . 1 101 . 1 
94.0 96.1 

96.9 96.8 



1 1.33 per cent magnetite. 

in continually increasing portions to a sand with 35.5 per cent 
of voids, the percentage of voids in the mixture was gradually 
reduced to a certain point corresponding to the voids to be filled, 
but on further addition they were again increased, as shown by 
the following figures. This point was reached when the dust 
amounted to 41 per cent of the sand, an amount greater than the 
voids; but this is due to the fact that the sand grains were un- 
avoidably separated to a very considerable extent by the dust and 
the voids consequently increased. 

WEIGHTS AND VOIDS IN NEW YORK SAND WITH VARIOUS 
PERCENTAGES OF 200-MESH DUST. 



Weight per 
Cubic Foot. 



Voids. 



Original sand, compacted hot. 

12.4% of dust 

16.7" ' 
20.6" ' 
24.2" ' 
30.4" ' 
36.0" ' 
41.7" ' 
50.0" ' 



106.0 
114.0 
116.0 
120.2 
127.0 
130.0 
132.5 
133.1 
114.6 



35.5 
31.0 
29.1 
26.6 
23.0 
21.2 
20.0 
19.7 
24.7 



THE MINERAL AGGREGATE. 



83 



When the densest of these sand and dust mixtures is added to 
a gravel with voids of 35.1 per cent in amount sufficient to fill the 
voids in the latter they are further reduced to about 12.1 per cent, 
and the aggregate weighs 144.8 pounds per cubic foot as compared 
to 164.1 pounds for solid quartz. 

WEIGHT PER CUBIC FOOT AND VOIDS IN CRUSHED FLINT, 
GRADED LIKE THE AVERAGE SAND IN SEVERAL CITIES, 
COMPARED WITH THE LOCAL SANDS OF THESE CITIES 
OF THE SAME GRADING, WITH NO 200-MESH MATERIAL, 
WITH 13 PER CENT OF 200-MESH FLINT AND 13 PER CENT 
OF 200-MESH DUST. SPECIFIC GRAVITY OF FLINT = 2. 65. 



Without 200- 
Mesh Material. 



With 200 Flint. 



Wt. per 
Cu. Ft. 



Voids. 



Wt. per 
Cu. Ft. 



Voids. 



With 200 Dust. 



Wt. per 
Cu. Ft. 



Voids. 



New York— 1898: 

Local 

Flint 

Chicago— 1898: 

Local , 

Flint 

St. Louis— 1899: 

Local 

Flint 

Louisville— 1899 : 

Local 

Flint 

Kansas City— 1898 : 

Local 

Flint 

Omaha— 1899 : 

Local 

Flint 

Trenton— 1898: 

Local , 

Flint 

Paterson— 1899: 

Local 

Flint 

Washington— 1899: 

Local 

Flint 

Buffalo— 1899: 

Local 

Flint 

Philadelphia— 1899: 

Local 

Flint 



109.6 
105.5 

109.1 
103.4 

111.9 
103.6 

104.5 
99.6 

110.4 
103.0 

113.3 
105.3 

111.1 
107.6 

110.6 
104.3 

106.1 
109.0 

109.6 
100.1 

107.8 
104.5 



34.1 
38.1 

34.6 
37.4 

31.7 
37.1 

36.0 
39.5 

32.5 
37.6 

30.9 
36.2 

31.6 
34.8 

32.6 
36.8 

36.5 
34.0 

33.9 
39.4 

35.2 
36.7 



115.6 
109.0 

113.9 
104.9 

116.1 
108.3 

110.9 
107.0 

115.0 
106.2 

118.6 
106.6 

117.1 
112.6 

115.6 
109.4 

114.5 
113.5 

115.9 
103.9 

111.3 
106.5 



30.5 
34.0 

32.3 
36.4 

29.1 
34.4 

32.1 
35.2 

29.9 
35.7 

27.6 
34.2 

28.2 
31.8 



29 
33 



31.4 
31.8 

30.1 
37.1 



33. 
35. 



118.9 
110.9 

120.4 
107.4 

122.2 
111.8 

115.7 
112.2 

122.4 
113.5 

124.5 
113.5 

123.5 
116.0 

121.0 
112.4 

119.0 
118.1 



120. 
108. 



119.4 
113.9 



26.5 
32.9 

27.9 
34.9 

25.4 
32.3 

29.1 
32.0 

25.3 
31.0 

24.0 
31.2 



24 
29 

26 
31 

28. 
26 

27. 
34. 

28. 
31. 



84 



THE MODERN ASPHALT PAVEMENT. 



Sharp as Compared with Rounded Sand. — If particles of the 
crushed quartz of sizes corresponding to those found in natural 
sand are combined in the proportions found in the latter, and the 
voids in each determined, the results are a striking illustration 
of the difference in the degree to which compaction can be carried 
with sand made up of sharp and rounded particles. (See preceding 
table, page 83) 

As in the case of the single-sized particles the sharp sands do not 
compact as well as those with rounded particles, and as the greatest 
possible compaction is desirable, it seems that a rounded sand is 
more suitable for the construction of asphalt pavements than a 
sharp one. Experience has shown that this is the case. The 
particles should, however, be rounded and not round, as in the 
latter case they would move too easily on one another and give 
the pavement a tendency to displacement under traffic. It will 
not do, however, to draw too general conclusions from a determina- 
tion of voids in a sand alone. Small voids are desirable, but may 
at the same time occur in sands which are unsuitable for use in a 
surface mixture. For example, sands too coarse to permit of 
being employed may have a smaller volume of voids than a finer 
or more suitable sand. 





Passing Mesh. 


Total. 


Wt per 
Cu. Ft. 


Voids 




200 


100 


80 


50 


40 


30 


20 


10 




Trenton 

Philadelphia. 






11 
22 


14 

18 


25 

30 


14 
14 


12 

7 


13 
5 


11 

4 


= 100% 
= 100% 


111.1 
107.8 


31.6 
35.2 



Here the coarse sand has the smaller volume of voids, which is 
quite often the case, but the size of the voids is too large and the 
sand is consequently undesirable. It is therefore necessary to 
consider the grading of a sand as well as its voids in judging it. 

Grading of Sands. — The proper grading for an asphalt mix- 
ture is seldom found in a single sand, but it can be arranged by 
mixing two or more containing particles of different sizes. The 
character of the sands which have been used in mixtures in various 
cities is illustrated by the following examples. 



THE MINERAL AGGREGATE. 
SAND GRADING— VARIOUS CITIES. 



85 



Cities. 







Passing Mesh. 






200 


100 


80 


50 


40 


30 


20 


10 


10 
2 


68 
15 


15 
17 


5 
52 


2 

9 








2 


2 


1 


2 


1 


4 


53 


25 


10 


3 


2 


32 



33 
1 


13 
2 


18 
36 


3 
32 


1 

17 






9 


3 


2 


25 


29 


36 


4 


3 


1 




2 


19 


19 


41 


12 


3 


2 


2 


2 


14 


26 


49 


6 


2 


1 




6 


13 


14 


31 


20 


10 


4 


2 





1 


1 


48 


46 


3 


1 





14 


26 


14 


38 


6 


2 






2 


4 


22 


28 


19 


10 


10 


5 


17 


40 


30 


10 


1 


1 


1 




31 


39 


21 


8 


1 








2 


9 


36 


49 


3 


1 






1 


6 


10 


41 


19 


15 


5 


3 



Total. 



Chicago — fine, 1896 

' ' — medium 

Louisville — river 

—bar 

Milwaukee — coarse beach. . . 
—White Fish Bay 
Omaha — single sand, 1899. . 
Shelby — single sand, 1899. . . 
Boston — single sand, 1899. . 

St. Louis — coarse, 1897 

—fine, 1897 

1 ' — river, coarse 

" — " fine 

Buffalo — bank, fine 

1 ' — lake, fine 

" — " coarse 



100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 
100% 



The preceding data show the very great variations in the charac- 
ter of different sands, not only as to the size and shape of the 
grains, which are of the utmost importance in preparing a surface 
mixture, but also in the character of the surface of the grains. It 
does not seem too much to say, therefore, that the selection of a 
suitable sand or the combination of two or more in a proper way is 
as important a detail in producing a satisfactory asphalt pavement 
as the regulating of any of the other constituents. The difficulties 
to be met with are numerous and demand experience in meeting 
them. 

Stone. — Stone is sometimes used as a part of the mineral 
aggregate, and this use has grown of late years. When it forms the 
chief portion of the wearing surface the latter is known as an 
asphaltic concrete. This material will be considered in a later 
part of this volume. 1 • 

SUMMARY. 

In this chapter the very varied character of the sand which is 
the chief constituent of the mineral aggregate of an asphalt surface 



1 Page 375. 



86 THE MODERN ASPHALT PAVEMENT. 

mixture has been shown, and that skill is necessary in selecting this 
material for the preparation of a satisfactory mixture. Sands differ 
according to their origin and the source from which they are 
obtained. They differ as regards the size of the grains of which 
they are made up, the relative proportion of different sized grains 
which are present, the shape of the grains, the character of the 
surface and of the material of which they are composed, and 
the proportion of the voids or vacant spaces between the grains 
when compacted. They also vary in their volume weight, a 
matter of importance where materials are mixed by weight and 
not by volume. 

Altogether there seems to be nothing more important for the 
construction of a satisfactory asphalt surface mixture than a 
thorough understanding of the peculiarities of the various sands 
and of their adaptability to the purpose for which they are used. 



CHAPTER IV. 
FILLER, OR DUST. 

A filler, or dust, is made a part of the mineral aggregate of 
asphalt surfaces for the purpose of rendering the surface more 
dense, so that it will be less acted upon by water, and less liable to 
interior displacement or movement. Its presence in a surface 
mixture may be looked at in much the same way as that of the 
finer clay particles in a soil. In fact soil physics, as treated by 
the agricultural physicists, is in many directions instructive as 
applied to surface mixtures, which are aggregates of small particles 
like soils and contain more or less bitumen as the soils do more or 
less water. 

In regard to the different parts played by fine and coarse 
particles in a soil, Whitney remarks : 1 

"In a symmetrical arrangement of the grains in a soil con- 
taining 47.64 per cent 2 by volume of empty space, each grain will 
touch the surface of six adjacent grains. There is a certain 
amount of surface attraction between these particles. 

"If the grains are large they still only touch at six points, and 
the weight of the grains is sufficient to overcome this slight sur- 
face attraction. A lump of wet sand will fall apart as it dries, 
for it is bound together by the contracting power of the film of 
water which surrounds it, and when this is removed by evapora- 
tion the weight of the grains is sufficient to overcome the surface 
attraction of the relatively large and heavy particles and they 
fall apart. 

1 Bulletin No. 4, U. S. Weather Bureau, 1892, 27. 

2 Whitney is, of course, wrong in assuming this volume; the voids, &£ 
has been shown on page 74, might be 25.95 per cent. 

87 



88 THE MODERN ASPHALT PAVEMENT. 

"If the grains are very small, like grains of clay, the surface 
attraction of the grains is sufficient to bind the mass into a com- 
pact lump when dry; for while there are still only six points of 
contact for any one grain, there are many other grains and so many 
more points of contact in a given weight of material. If the size 
of the grains was still further reduced to molecular proportions 
the mass would assume the hardness and rigidity of a single grain 
of sand or clay." 

These facts apply as well to asphalt-surface mixtures as to 
soils, and explain the parts which a filler plays. 

This, however, has been little understood heretofore in the 
paving industry. 

Dust in the Earlier Days. — In the earlier days of the industry, 
and even as late as 1885, the Washington specifications for asphalt 
pavements read that the mixture shall contain 12 to 15 per cent 
of carbonate of lime and that "the powdered carbonate of lime 
will be of such a degree of fineness that 16 per cent by weight 
of the entire mixture for the pavement shall be an impalpable 
powder of limestone and the whole of it shall pass a No. 26 screen. 
The sand will be of such size that none of it will pass a No. 80 
screen and the whole shall pass a No. 20 screen." As a matter 
of fact, very little real dust, 200 mesh, was put in the mixture 
and it was a question even as late as 1893 whether dust con- 
tributed in any way to improve it. 

That it is of the greatest value, especially in surface exposed 
to heavy traffic, is now known. The difference in the penetra- 
tion, ductility, and resistance to stress of the same bitumen with 
and without filler can be readily shown. 1 Filler, therefore, enables 
us to use a softer cement than otherwise would be the case and 
thus make an asphalt surface less liable to mark in hot, less brittle 
in cold weather, and far less liable to internal displacement. In 
the earlier asphalt pavements where Trinidad asphalt was the 
only cementing material in use this contained in itself so much 
fine inorganic matter which was a natural filler that it was a great 
help to the surface before the necessity for the presence of a high 
percentage of dust was understood. 

* See page 373 



FILLER, OR DUST. 89 

The use of a filler is well illustrated in the laying of coal-tar 
walks in England, where very soft coal-tar is mixed with all the 
slaked lime it will hold, often more than 50 per cent by weight, 
and this mixture used as a cement with sand. The filler makes 
it possible to use a tar so soft that it will not crack in winter, while 
preventing its marking excessively in summer. 

Varieties of Filler. — Numerous kinds of mineral matter, ground 
to a more or less fine powder, have been used from time ta time 
in asphalt mixtures as a filler. These include 

Limestone, Natural hydraulic cement, 

Hydraulic limestone,- Portland hydraulic cement, 

Trap rock, Clay, 

Volcanic, Ground shale, 

Marl, Dust-collector dust, 

Silica, Ground waste lime from beet- 

Caustic or slaked lime, sugar factories. 

Ground Limestone has been used far more than any other and 
was the original material employed by De Smedt. There is prob- 
ably nothing better than this, unless it be Portland cement, for 
heavy- traffic streets. It is a desirable material, as asphalt cement 
adheres to it firmly and does so by being absorbed by it to a cer- 
tain extent. 

Ground hydraulic limestone has also been used where it could 
be conveniently and cheaply obtained from the cement manu- 
facturers. It is, no doubt, as suitable for its purpose as the simple 
carbonate. 

Ground Shale. — In the manufacture of shale bricks the shale is 
first ground to a powder which is often extremely fine and in con- 
sequence suitable for use as a filler. Such a shale dust is available 
in the State of Washington, 91 per cent passing a 200-mesh screen 
and 79 per cent remaining suspended in water for fifteen seconds. 
Ground Clay or loam free from organic matter could also be 
used in a similar way. A large part of the natural filler in Trinidad 
asphalt is clay, and on this account it was thought that clay might 
eventually prove the most desirable filler, as owing to its peculiar 
surface and porosity it will absorb bitumen much more satisfac- 
torily than any of the ground rock fillers, but it has been found to 
have such a small volume weight and to be so light and fluffy that 



90 THE MODERN ASPHALT PAVEMENT. 

a large part of the clay is blown away in an open mixer and it can 
only be used successfully in a tightly-closed one, which is rarely 
available. In this connection the studies of Dr. A. S. Cushman, 
of the Office of Public Roads, U. S. Department of Agriculture, 
on "The Nature of Clay" and on "The Adsorption of Solids by 
Rock Powders" are of great interest. 

Ground Waste Lime from Beet-sugar Factories. — In the process 
of defecating the diffusion liquors obtained in the extraction of 
sugar from beets large quantities of caustic lime in the form of 
cream of lime are used, which is subsequently removed from the 
sugar solution by nitration. This when dried and ground has been 
suggested for use as a filler and employed to a small extent in 
California and Michigan. As far as fineness is concerned it is a 
satisfactory material, but it contains many impurities such as 
organic matter in the form of sugar and organic acids combined 
with lime. Analysis shows that it has the following composition: 

COMPOSITION OF DRIED AND POWDERED BEET-SUGAR 
FILTER-PRESS CAKE. 

Calcium carbonate 78 . 0% 

Free lime 1.0 

Lime combined with organic matter 5.0 

Magnesia carbonate 2.0 

Alkalies 2 

Iron and alumina 2.6 

Sulphuric, phosphoric, and oxalic acids 2.4 

Sugar „ 5.0 

Organic not sugar 2.1 

98.3 

It is to a certain extent an open question whether the organic 
matter will prove deleterious to the surface mixture and the free 
lime likewise. Experience alone can prove the availability of 
this material as a filler. 

Ground Marl has served of late years as a filler in those cities 
near the marl-beds of Ohio and Michigan. It gave fairly satis- 
factory results, but its disadvantage lies in its low volume weight, 
in consequence of which it is readily blown away on mixing it with 
sand, and its use has been discontinued. 

Ground Silica. — Ground sand and trap-rock have been largely 
used in the work in New York. It is questionable if it is desirable 



FILLER, OR DUST. 91 

as a substitute for limestone, as asphalt does not adhere to it as 
well and it cannot be ground as fine. It is a filler, however, and 
successful results have been obtained with it. 

As between ground limestone and silica or silicate dusts, experi- 
ments of Mr. F. P. Smith, formerly of the Alcatraz Asphalt Co., 
have shown that the former enables a mixture made with it to 
resist water action better than the silica filler, and this can be 
readily understood for the reason that has been given, namely, 
that bitumen will adhere to the former much more firmly than to 
the latter by being partly absorbed by it. 

Caustic and Slaked Lime. — These fillers have only been used 
experimentally. They are largely employed in coal-tar work. 
No peculiarities have been noticed in the small amount of work 
done with them, but in the laboratory cylinders of surface mixture 
containing caustic lime expanded badly on immersion in water. 
It would probably not be desirable to experiment further with 
their use. 

Natural Hydraulic Cement. — This material began to be used 
as a filler in cases where limestone dust was not available. How- 
ever, of late years its use has been abandoned, as it has been observed 
that surfaces laid with this material as a filler have cracked more 
than where limestone was the ground material. It seems to 
possess the property, perhaps owing to the presence of free lime, 
of hardening the asphalt cement very rapidly. If it is necessary to 
use such a filler the cement should be at least 20 points softer than 
would be the case with other materials. 

Portland Cement. — This is a material which, for some reason 
not yet satisfactorily explained, gives the best results as a filler in 
asphalt surfaces, especially on streets of heavy traffic or where 
the surface is subject to the action of water. Its desirability 
may be due to its capacity for adsorbing a thick film of bitu- 
men, but it cannot with certainty be attributed to its hydraulic 
properties. 

A cylinder of open Trinidad asphalt surface mixture, made up in 
Washington, D. C. ? in 1894, half of which contained limestone 
dust as a filler and the other Portland cement, showed the most 
striking contrast in its appearance after nearly six years' immersion 



92 THE MODERN ASPHALT PAVEMENT. 

in water, the portion containing Portland cement being still hard 
and firm, while the ordinary limestone mixture was much more 
strongly acted upon. 

The slight extra cost of Portland cement is more than made 
up by the improvement in the character of the surface, where 
especially trying conditions are to be met, and its use is highly to 
be commended. 

Fine Grinding of the Filler. — The material which is of value in a 
filler is the impalpable dust, much finer than the particles merely 
passing a 200-mesh sieve. Sandy particles of dust of about the 
200-mesh size are probably of somewhat greater value than the 
200-mesh rounded particles of an ordinary sand, which are at 
times distinctly disadvantageous in a mixture, as they are 
sharper. Larger particles do not differ from sand grains of the 
same size. 

It is important, therefore, in securing a filler that it should 
contain as much real dust as possible. If there is only 45 per 
cent of this material, twice as much must be used as if it contained 
90 per cent. In the former case the sand must be heated to a 
much higher temperature to take care of so much cold material, 
while in the other, as a matter of economy, the smaller bulk to be 
handled to accomplish the same object is an important con- 
sideration. 

As it is difficult to find a desirable filler on the market, dust 
should be ground by paving companies themselves. It can be 
turned out with a tube-mill 85 to 95 per cent fine. There is no 
question but that the production and use of such dust will pay 
if for no other reason than to do away with the excessive cooling 
of the mixture caused by the addition of the large quantities of 
cold, coarse material to the sand which are necessary to obtain 
a sufficient amount of true filler. 

More Refined Methods of Examining Filler. — Up to the prepent 
point fillers have chiefly been spoken of, as to their fineness, accord- 
ing to the amount which will pass a 200-mesh sieve, the finest 
wire sieve that is made. As has been said, the material passing 
this sieve may be much of it sand smaller than .10 mm. in diam- 
eter, and very little of it may be true dust or filler of a diameter 



FILLER, OR DUST. 93 

smaller than .025. The difference in character of the two sizes 
is readily seen on inspection. 

In judging the value of a filler it is desirable to determine the rela- 
tive amount of these materials, coarse material, and the impalpable 
dust. As there are no finer sieves than the 200-mesh, this can only 
be done by elutriation, or washing with water, the coarser grains 
settling out rapidly and the finer more slowly. The manner of 
doing this is as follows: 

Five grams of the dust to be examined are placed in a beaker 
about 120 mm. high, holding about 600 c.c. The beaker is nearly 
filled with distilled water, at a temperature of exactly 68° F., 
and agitated with an air-blast until the dust and water are thor- 
oughly mixed, taking care net to produce cyclonic currents in 
the latter. On stopping the blast the liquid is allowed to stand 
exactly 15 seconds and the water above the sediment immediately 
decanted without pouring off any of the latter. This washing 
is repeated three times. The sediment is then washed out into 
a dish, dried, and weighed. The loss in weight represents that 
portion which may be considered as dust free from sand. The 
washing must be done with distilled water and at a definite tem- 
perature. 

This method can also be used with hydraulic cements or mate- 
rials acted upon by water, since the finer portion is the only part 
acted upon, while the coarser part, which is recovered and weighed, 
is not acted upon at all. 

The differentiation of the particles not subsiding in 15 seconds 
can be carried further, if desired, by reagitating the decanted 
liquid and allowing the sedimentation to go on for 1 minute, 30 
minutes, 1 hour, and so on. For ordinary purposes this is unneces- 
sary. 1 The size of the particles obtained by elutriation can be 
measured in the same way as that of the particles passed by 
the finer sieves, as described by Hazen. The size of these 
particles among ordinary fillers will be found in the following 
table : 

1 For further details, see Hazen, 24th Annual Report Massachusetts State 
Board of Health, 1892, 541. 



94 



THE MODERN ASPHALT PAVEMENT. 



VOLUME WEIGHT OF DUST. 



Test number . 
Dust 



Passing 200-mesh. 

100- " . 

80- " . 

50- " . 



Elutriation test not set- 
tled in 15 seconds 

Pounds per cubic foot. . . . 



75803 


75804 


75805 


75806 


71076 


Lime- 
stone 


Trap 
rock 


Port. 

cement 


Clay 


Marl 


84.0% 
14.0 
2.0 


81% 
18 

1 


74% 
19 

6 

1 

56.7% 


93% 
5 
1 
1 

87.8% 


92% 
4 
2 
2 

80.3% 


71.3% 


70.3% 


113.7 


112.3 


123.5 


78.0 


78.0 



75791 

Vol- 
canic 

100% 



98.2% 
63.4 



A number of dusts from various parts of the country have been 
differentiated and the results are as follows : 

SIZE OF PARTICLES IN VARIOUS FILLERS. 



Test No. 


Character. 


Per Cent 

Passing 

200. 


Per Cent 
on 200. 


30915 


Limestone. 


96 


4 


30963 


Sili-a. 


96 


4 


30267 


Limestone. 


91 


9 


30578 


< < 


93 


7 


30715 


" 


48 


52 


30716 


< ( 


66 


34 


30766 


Silica. 


67 


33 


30606 


Marl. 


91 


9 



In these fillers, as supplied for use, there was present 
the percentages of particles passing a 200-mesh sieve shown in 
the preceding table. 

This 200-mesh material consists of the following sized par- 
ticles: 



FILLER, OR DUST. 



95 



Time of 


Average 

Size of 

Particles 


Test No. 


Subsidation. 




















Less than 


30015 


30963 


30276 


30578 


30715 


30716 


30766 


30606 


Difference and 




















loss 


.001 mm. 


4.4 


1.0 


3.8 


.4 


2.7 


11.9 


3.2 


2.4 


16 hours 


.0025 " 


2.8 

5.0 

51.3 


4.2 
2.9 

42.4 


4.9 
55.1 


5.4 

67.4 


3.1 
32.5 


3.2 

23.9 


3.0 
23.3 




2 " 


.0075 " 


7.7 


30 minutes. . . 


.025 " 


66.5 


1 minute 


.050 " 


17.7 
18.8 


9.3 
40.2 


15.0 
21.2 


12.9 
13.9 


24.8 
36.9 


20.1 
40.9 


25.6 
44.9 


13.0 


15 seconds. . . . 


.080 " 


10.4 




100.0 


100.0 


100.0 


100.0 


100.0 


100.0 


100.0 


100.0 


Actual dust in 




















original ma- 
terial small- 




















er than 


.050 " 


78.0 


55.6 


71.7 


80.1 


30.3 


39.0 


36.9 


80.5 



As showing the variation in the amount of material which 
is not ground even fine enough to pass a 200-mesh sieve the first 
data given may be examined. The coarse material varies from 
4 per cent in high-grade fillers to 52 per cent in an inferior article. 
Separating out and rejecting this coarse material as of no value 
greater than that of sand the finer grains were separated by elu- 
triation into the particles of the sizes given. 

It seems fair to consider that particles smaller than .050 mm. 
in average diameter are the only portions of a filler to be con- 
sidered as true dust, and it will be seen that of the entire mate- 
rial in several instances only 30-40 per cent is dust and the remain- 
der sand. 

A good filler should contain at least 60 per cent of its weight 
of actual dust and preferably over 70 per cent. 

An examination of a filler or even a mixture in this way is 
very serviceable in revealing the actual amount of fine dust which 
either may contain. In a mixture examined in New York the 
actual amount of dust of different sizes is shown in the following 
analysis: 



96 



THE MODERN ASPHALT PAVEMENT. 



TEST NO. 30954. 
Bitumen 11 .0% 



200. .. 



100. 
80. 
50. 
40. 
30. 
20. 
10. 



Settling in, 
Time. 

Difference, 
or loss. . 

2 hours. . . 
30 minutes. 

1 minute.. 
15 seconds. 



Size of 
Particles 
Less than 



.0075 mm. 
.025 " 
.050 " 
.080 " 



•8%. 

.3 . 

2.5 . 

4.2 . 

10.2 . 

18.0 



14.0 

15.0 

25.0 

10.0 

2.0 

3.0 

2.0 

100.0 



200 Mesh 

on 100 

Per Cent 

Basis. 


4.2% 
1.6 


13.8 


23.8 


5&. 6 



100.0 



Sand 77.6% 

Dust 5.4 

Trinidad A. C 17,0 

100.0 

The dust was the finest-ground limestone of the composition 
given in the preceding table. It contained, as used, 81.2 per 
cent of particles not subsiding in 15 seconds. From the amount 
of dust in use it is readily calculated that no more than 4.3 per 
cent of material which acts as a filler would be expected in the 
mixture. 7.9 per cent is actually found, the excess over the cal- 
culated 4.3 per cent being due to the fine material derived from 
that in the Trinidad asphalt. The small percentage of real dust 
in some of our mixtures is therefore striking. 



SUMMAEY. 

The character of the filler or finely ground inorganic matter 
which enters into the composition of the mineral aggregate of 
an asphalt surface has been shown in the preceding chapter to 
be a matter of very considerable importance. Impalpably fine 
mineral matter of various kinds can be satisfactorily used, but 
it should be as fine as possible, and for construction of an asphalt 



FILLER, OR DUST. 97 

pavement on streets of heavy travel Portland cement should alone 
be used as a source of supply. 

The intelligent use of filler in an asphalt surface mixture demands 
further careful consideration from a physical point of view, and 
the investigations which have been carried on in regard to rock 
powders in the Office of Public Roads, U. S. Department of 
Agriculture, have thrown much light upon this subject. 



CHAPTER V. 

THE NATURE OF THE HYDROCARBONS WHICH CONSTITUTE 
THE NATIVE BITUMENS. 

Asphalt cement is the distinctive feature of an asphalt pave- 
ment. It serves to bind the mineral aggregate together and 
enables it to carry traffic without displacement. 

It consists of some native asphalt or other hard native bitu- 
men, fluxed with some soft bitumen in the form of dense petro- 
leum oil or maltha, or of some hard residue from the distillation 
or treatment of asphaltic petroleum, softened to a proper con- 
sistency in the same way. 

Asphalt cement is, therefore, native bitumen and its intelli- 
gent consideration necessitates a knowledge of and the differentia- 
tion of the various native bitumens of which it may be made up. 

The hydrocarbons, or compounds of hydrogen and carbon, 
which when mixed in varying proportions constitute the sub- 
stances which are known as bitumen, belong to different series, 
so called, which are characterized by the relative proportion of 
hydrogen and carbon atoms which they contain and by their 
structure or the relation of the carbon atoms to one another in 
space. A short explanation in regard to the structure of the 
various hydrocarbons of these series is necessary for an intelli- 
gent understanding of their properties as affecting the character 
of the bitumen in use in asphalt pavements. 

Chain Hydrocarbons. — The carbon atom is characterized 
chemically as being quadrivalent; that is to say, it possesses four 
affinities, bonds, or links by means of which it may be said to 
combine with atoms of other elements. The hydrogen atom 
has but one bond and is univalent. 

98 



NATURE OF THE HYDROCARBONS. 99 

If a carbon atom combines with all the hydrogen atoms that 
it is capable of, its four bonds must each be linked with a hydrogen 
atom, and the resulting molecule will consist of one atom of car- 
bon and four of hydrogen, which can be represented by the symbol 
CH 4 , in which C stands for one carbon atom and H 4 for four hydro- 
gen atoms. In this substance or compound, which is known 
as methane, or marsh-gas, we have the carbon atom saturated 
as to its affinities, or bonds, with hydrogen atoms. It cannot 
combine with any other atom except by replacing with it one 
or more of the hydrogen atoms. It is, therefore, known as a 
saturated hydrocarbon. 

If two, three, or more atoms of carbon are combined in the 
same way to form a molecule having C2 or C3, etc., in its com- 
position, these carbon atoms are themselves linked or bonded 
together by one or more of the bonds of each atom, so that we 
may have: 

One carbon atom with its four affinities or bonds which may 
be represented thus: 



1 

Two carbon atoms joined by one affinity of each thus] 

1 1 

— c— c— 

I I 

Or by two affinities of each thus: 

u 



In the case of two carbon atoms joined by one affinity each, 
there are six bonds remaining to unite with hydrogen. The result- 
ing compound with hydrogen in this case is represented by the 
symbol or formula C2H 6 . It is a saturated hydrocarbon in the 
same way that CH 4 , with one atom of carbon, is, because, while 
two bonds out of the eight of the two carbon atoms are necessarily 



100 THE MODERN ASPHALT PAVEMENT. 

joined in linking the carbon atoms together, all the remaining 
available affinities are satisfied by hydrogen. In the same way 
with three atoms of carbon in the molecule we have the carbon 
atoms linked to each other, so that eight affinities out of 
twelve remain to be saturated by hydrogen thus: 

H H H 
H— C— C— C— H 

One atom is, of course, linked to two others, and so two affini- 
ties of this atom are not available for combining with hydrogen. 
This saturated hydrocarbon is represented by the symbol CsH 8 . 

As the carbon atoms increase in number there is found to be 
a regular increase in those of hydrogen, so that the compounds of 
this saturated nature become what is called a homologous series, 
differing by one carbon and two hydrogen atoms from the 
following and preceding. 

CH4, C2H 6 , CsH 8 , C n H 2n +2« 

If in any of these simple chain hydrocarbons, which owing 
to the simplicity of their constitution are known as normal hydro- 
carbons, one of the hydrogen atoms is supposed to be removed, a 
group is left with one free affinity, or if two hydrogens or more 
are removed, with two or more affinities. These imaginary groups 
of atoms with different affinities are known as radicals. They 
can combine with other similar radicals or with other elements, 
such as the halogens, or with acid radicals. Thus we may have 

CH4 — CH3 =CH2 =CH 

Saturated. Methyl. Methylene. Methenyl. 

If different hydrocarbon radicals are substituted for hydrogen 
in other hydrocarbons new hydrocarbons result. In this way 
hydrocarbons are produced which have the same composition 
or number of carbon and hydrogen atoms as in the normal hydro- 
carbon, but a different structure. For pentane, therefore, C 5 H 12 * 
there may be three forms: 






NATURE OF THE HYDROCARBONS. 101 

CH3 — CH2 — CH2 — CH2 — CH3 

CH3 — CH — CH2 — CH3 

I 
CH 3 

CH 3 

H3C— C — CH3 

I 
CH 3 

Here the straight chain is converted into one with one or more 
radicals known as side-chains. 

These hydrocarbons are denominated normal pentane, iso- 
pentane, and tetramethylmethane, the latter being methane in 
which the four hydrogen atoms are substituted by methyl groups. 
They are also known as isomers, since they contain the same num- 
ber of carbon and hydrogen atoms; that is to say, have the same 
percentage composition but a different structure and different 
physical properties. 

With similar hydrocarbons in which the carbon atoms are 
greater in number the possible variations in structural arrange- 
ment are much more numerous, and it can be readily seen that 
the number of different paraffine hydrocarbons is enormous. 

These compounds of carbon and hydrogen illustrate what 
is meant by a series of hydrocarbons, which is, in this case, a satu- 
rated series known as the paraffine, limit, or chain series, since 
the carbon atoms are represented as linked in the form of a chain. 
It is the series which makes up the greater part of ordinary Penn- 
sylvania and Ohio petroleum and the residuum made from these 
oils. 

In this series, the carbon being combined with as much hydro- 
gen as possible, there is the largest percentage of hydrogen and 
the smallest percentage of carbon found in any hydrocarbons 
of a given number of carbon atoms. For marsh-gas, CH 4 , it 
is 75 per cent carbon and 25 per cent hydrogen, a proportion 
gradually diminishing as the number of carbon atoms increases. 
For example, for C3oH 62 it is carbon 85.31, hydrogen 14.69. 



102 THE MODERN ASPHALT PAVEMENT. 

Unsaturated Hydrocarbons. — When the carbon atoms in a 
hydrocarbon do not combine with all the hydrogen atoms they 
might, the remaining affinities are satisfied in joining the carbon 
atoms together, in addition to the single bond found in the satu- 
rated series. The linking of the carbon atoms is then doubled 
and the hydrocarbons may be represented thus: 

H H H H 

II II 

C=C C=C— C— H 

II III 

H H H H H 

Owing to the double bond, two affinities which in the unsatu- 
rated series were combined with hydrogen, are now linked with 
each other and a new series is determined in which the hydrogen 
atoms number always twice the carbon atoms. The affinities of 
the carbon are not entirely satisfied with hydrogen, and the hydro- 
carbons are known as unsaturated hydrocarbons. As the rela- 
tion of carbon to hydrogen is constant the percentage composition 
of all the hydrocarbons of the C n H 2ri series is carbon 85.71, hydro- 
gen 14.29, the amount of hydrogen being always less than in any 
of the hydrocarbons of the saturated series containing the same 
number of carbon atoms. 

In this series, which is known as the Olefine Hydrocarbons, 
but two of the carbon affinities are joined by a double bond. More 
of these affinities may be joined in this way, resulting in other 
series represented by the general formula C n H 2n _ 2> C n H 2ra _ 4 , 
C n H 2n _ 6 , etc., in which the per cent of hydrogen is still less. 

The hydrocarbons of these series, it is plain, are even more 
unsaturated. 

Hydrocarbons in general are divided, therefore, into those 
which are saturated and those which are unsaturated, the former 
being stable and the latter reactive and very susceptible to change, 
combining with or being converted into other hydrocarbons by 
the action of sulphuric acid and other reagents. The saturated 
can be separated from the unsaturated hydrocarbons by strong 
sulphuric acid, and this will be found to be a very important means 
of differentiating the oils and the solid bitumens among them- 



NATURE OF THE HYDROCARBONS. 103 

selves, by determining the relative proportions of these two classes 
of hydrocarbons which they contain. 

Cyclic Hydrocarbons. — In the preceding hydrocarbons the 
carbon atoms have been imagined as being linked in the form 
of a chain of more or less simplicity. It can readily be imagined 
that the normal chain can be bent into the form of a circle so 
that the carbon atoms at the ends may be united with each other 
by one of each of their three affinities. In this way a ring is formed, 
each carbon atom of which has only two affinities unsaturated, 
but which possesses no double bond when these affinities are all 
satisfied with hydrogen, so that although its general formula is 
C n B.2n, the same as that of the unsaturated olefines, they are 
saturated hydrocarbons. 

Owing to reasons which it is unnecessary to go into in this 
place the carbon atoms in such a ring do not exceed seven in num- 
ber, as above that they would be quite unstable and could not 
exist. The most stable rings are those of five and six atoms, and 
hydrocarbons with this number are the foundation or source of 
many of the solid native bitumens. Their structure may be 
represented as follows: 

CH2 — CH2\ CH2 — CH2 — CH2 

I ym 2 or C 5 H 10 I I or C 6 H 12 

CH2 — CH2 CH2 — CH2 — CH2 

Pentamethylene. Hexamethylene. 

The carbon-hydrogen groups of which they are made up are 
the groups or radicals known as methylene. 

For this reason the hydrocarbons are known as a class as the 
polymethylenes, pentamethylene being the hydrocarbon of five 
groups, hexamethylene the one of six. The generic name of 
naphthenes is also applied to the series, having been used to desig- 
nate the polymethylenes occurring in Russian petroleum before 
their structure was elucidated. They are distinguished by the 
fact that, although not as stable as the paraffine hydrocarbons, 
they still possess the stability of saturated compounds and are 
unacted upon by strong sulphuric acid. 

In these polymethylenes, as in the normal chain hydrocarbons, 
one or more of the hydrogen atoms can be substituted by radicals 



104 THE MODERN ASPHALT PAVEMENT. 

like methyl. We have, for instance, methylpentamethylene, in 
which one of the hydrogen atoms of one of the methylene groups 
in pentamethylene is substituted by CH 3 the methyl group: 

CH2 — CH2\ 

>CH— CH 3 
CH 2 — CH/ 

or 

C6H12 

It will be noted that this hydrocarbon has the same formula 
as hexamethylene and differs from it only in structure. They 
are isomers. 

More complicated chains can exist, as where the radical propyl 
C3H7 or others replace the methyl radical and the possibilities in 
number and isomerism is again immense. 

The more complicated single-ring polymethylenes with side- 
chains are more reactive than the simple naphthenes. 

Unsaturated Cyclic Hydrocarbons. — Corresponding to these 
so-called cyclic saturated hydrocarbons, in which the carbon 
atoms are only united with each other by one bond, unsaturated 
cyclic hydrocarbons exist in which double bonds occur. The 
most familiar hydrocarbon of this type is benzol, derived from 
coal-tar, which has the following structure: 

H 



H— C C— H 

I II 
H— C C— H 

\/ 
C 



k 



This forms a new series known as the benzol or aromatic series, 
the general formula for which is C n H 2n -6- 

These hydrocarbons occur in a greater or less degree in all 
petroleums, at least among the more volatile portions, and are 
particularly prominent in California and Russian petroleum. 






NATURE OF THE HYDROCARBONS. 105 

Where the number of double bonds is fewer than in the benzol 
ring other series of hydrocarbons are formed, known as the hydro- 
aromatic series, the hydrocarbons of which, in their constitution, 
are between the saturated polymethylenes and the aromatic com- 
pounds. The terpenes are members of this series, but they are 
not found in the solid native bitumens used in pavements. Hexa- 
hydrobenzol is the same thing as hexamethylene and is a saturated 
hydrocarbon. Tetrahydrobenzol is an unsaturated hydrocarbon 
corresponding in the cyclic series to the olefmes of the chain hydro- 
carbons. 

In all of these aromatic and hydrated aromatic hydrocarbons, 
as well as in the saturated polymethylenes, any or all of the hydro- 
gen atoms may be substituted by paramne or olefine radicals, 
thus making it possible to form a vast number of new hydro- 
carbons containing side-chains, of which toluol, or methyl benzol, 
is a type in the aromatic series, as was methyl pentamethylene 
in the polymethylene series. 

H 

I 
C 

/\ 

H — C C — CH3 CH2 — CH2\ 

I || I \ C _H-CH 3 

H— C C— H CH 2 — CH 2 / 

%^/ Methylpentamethylene. 

c 

I 

H 

Methylbenzol. 

Dicyclic Hydrocarbons. — The cyclic hydrocarbons thus far 
considered have consisted of but one ring. Dicyclic and poly- 
cyclic hydrocarbons are also known to exist in which two or more 
rings may be united by having carbon atoms in common, as in 
the case of naphthalene, CioH 8 , the result of the condensation 
of two benzol rings: 



106 THE MODERN ASPHALT PAVEMENT. 

H H 

i i 

H— C C C— H 

I II | orC 10 H 8 

H— C C C— H 

c c 

i A 

or of three rings, as in anthracene: 
H H H 

I I I 

c c c 

/\ /\ /\ 

H— C C C C— H 

I II II II 
H— C C C C— H 

\/ \/ \/ 

c c c 



or Ci 4 H 10 



H H H 

The latter substance may also be considered as consisting of 
two benzol rings united by two methenyl radicals. 

The benzol rings may also be united by free affinities or by 
one or more methylene radicals without common carbon atoms, 
as in diphenyl, CeH 5 — CeH 5 , as dibenzyl, CeH 5 — CH 2 — CH 2 — CeH 5 , 
stilbene, C 6 H 5 CH=:CHC 6 H5, or as tolane, C 6 H 5 C=C C 6 H 5 . 

These hydrocarbons are mentioned, not from their immediate 
interest in connection with the bitumens, as they only occur in 
coal-tar, but as showing the infinite variation in structure, which 
is possible. 

Polycyclic Polymethylenes. — In the polymethylene series 
bicyclic and polycyclic hydrocarbons also exist, in which two or 
more rings have common carbon atoms, but instead of two carbon 
atoms being common to both rings, as in naphthalene, three such 
are found in the bicyclic polymethylenes, forming what is known 
as a bridge structure. This is illustrated by two hydrocarbons 






NATURE OF THE HYDROCARBONS. 107 

prepared synthetically by Rabe and Weilinger 1 and having the 
following structure : 

CioHig C13H24 
CH 2 — C(CH 3 )— CH 2 CH 2 — CH CH 2 

II I I.I I -CH 3 

CH 2 CH 2 CH 2 CH 2 CH.CH 3 CH.CH 

II III I -CH3 

CH 2 -CH CH 2 CH 2 — CH CH 2 

Methyl-bicyclo-nonane. Isopropyl-methyl-bicyclo-nonane. 

The latter hydrocarbon has probably been found by Coates 
in Louisiana and by Mabery in Santa Barbara, Cal., petroleum, 2 
as can be seen from the close correspondence in the physical and 
other characteristics of the synthetic and native hydrocarbons. 





Synthetic. 


Louisiana. 


California, 


Specific gravity 


0.8646 


0.8629 


8621 


Refractive index 


1.460 


1.4692 


1.4687 


Molecular refraction: 








Found for C 13 H 24 , 


57.677 


57.93 


58.05 


Calculated , 


57.737 






Boiling-point, 755 mm. . , 


232 


235 




28 mm. . , 


132 


60 mm. 


150 


Ultimate composition: 








Carbon 


. . 86.48-86.56 


86.58 


86.68 


Hydrogen , 


. . 13.28-13.15 


13.42 


13.62 


Calculated: 








Carbon 


86.67 






Hydrogen , 


13.33 







The hydrocarbons of the heavier asphaltic petroleums are, 
therefore, probably bicyclic or bridge compounds in those of lower 
boiling point, and polycyclic in the higher ones. 

In the lightest oils from Trinidad asphalt a hydrocarbon has 
been isolated which has the same formula as the preceding ones, 
but differs from them in some of its characteristics, as can be seen 
from the data on the next page. 

This hydrocarbon, while in some respects like those prepared 
by synthesis and from the California and Louisiana petroleums, is 

1 Berichte der deutschen chemischen Gesellschaft, 1904, 37, 1667-1675. 

2 Coates, J. Am. Chem. Soc, 1906, 384. Mabery, Proc. Am. Acad., 1904, 
40, 340. 



108 THE MODERN ASPHALT PAVEMENT. 

HYDROCARBON FROM TRINIDAD ASPHALT. 

Specific gravity 8690 

Refractive index 1 .4721 

Molecular refraction, found 57 .98 

" " calculated 57.737 

Boiling-point, 30 mm 170-180° 

Ultimate composition: 

Carbon 86 .85 

Hydrogen 13 .34 

sharply differentiated from them by its much higher boiling point, 
and cannot, consequently, be of the same structure. The as- 
phalt hydrocarbons differ, therefore, from those found in the 
petroleums, but apparently are of a similar nature, and the low- 
est ones at least of the series, are probably substituted bi cyclic or 
bridge polymethylenes, the higher being polycyclic. The idea 
previously advanced by Markownikoff, Mabery and the author 
that they were probably two rings united by polymethylene groups, 
is seen to be untenable. 

Hydrocarbon Derivatives. — Hitherto hydrocarbons only have 
been described as constituents of the native bitumens, but there 
are other substances entering into their composition which con- 
tain, in addition to carbon and hydrogen, sulphur, nitrogen, and 
more rarely oxygen. They consist of cyclic compounds contain- 
ing an atom of sulphur or nitrogen in the carbon ring, compounds 
which are, in asphalt, dicyclic and polycyclic, and oxygen deriva- 
tives, probably polycyclic phenols, together with oxidation products 
of the hydrocarbons. As these constitute but a minor portion 
of native bitumen they will not be described in detail here. They 
can be readily separated from the hydrocarbons by appropriate 
reagents, but have not been closely studied. They are also found 
in various dense petroleums. 

The nature and structure of the hydrocarbons and their deriv- 
atives have been entered into with some detail since the relative 
proportion of the various series which are present in any petro- 
leum or solid bitumen has a strong influence on its characteristics, 
and, more especially, the relation of saturated to unsaturated 
hydrocarbons and of the parafhnes to polymethylenes, these con- 
siderations being, of course, quite apart from the relative amounts 
of liquid and solid substances, malthenes and asphaltenes, upon 



NATURE OF THE HYDROCARBONS. 109 

which the consistency of the bitumen, but not its chemical char- 
acteristics, are based. 

The saturated hydrocarbons, especially those of the parafhne 
series which are found in the residues from the distillation of 
Pennsylvania petroleum and of those from Ohio, Kentucky, Kansas, 
and similar oils, are most stable. They are not readily attacked 
by strong acids, alkalies, or water They form by far the largest 
part of the residuums derived from these petroleums. The satu- 
rated hydrocarbons of the polymethylene series found in some 
residuums as well as in the solid bitumens are not attacked by 
acids or water, but are readily condensed by the abstraction of 
hydrogen under certain other conditions. The polymethylene 
hydrocarbons or the petroleums containing them are in this way 
the primary source of all asphalts. No asphalt can originate in 
nature in a paramne oil, but all polymethylene oils leave an as- 
phaltic residue on weathering or on evaporation or distillation 
with heat. 

No solid native bitumen suitable for paving purposes is known 
which contains parafhne, while the relative proportions . of satu- 
rated and unsaturated hydrocarbons in them may be very variable. 

The characterization of heavy oils or of solid bitumens and 
their differentiation is, therefore, arrived at by determining by 
appropriate analytical methods and by treatment with reagents 
the relative proportion of the malthenes and asphaltenes present, 
the proportions of saturated to unsaturated hydrocarbons in 
the malthenes, and the characteristics of all these classes of bitu- 
mens. The asphaltenes are probably composed entirely of unsat- 
urated or unstable compounds. 

SUMMARY. 

For a thorough understanding of the nature of the native bitu- 
mens the constitution of the various hydrocarbons of which they 
may be composed has been outlined in the preceding chapter. 
This involves some knowledge of chemistry and may, therefore, 
be" somewhat unintelligible to the general reader, but the state- 
ments here presented are entirely necessary in any treatise which 
aims at being at all complete in its consideration of the subject 
of the native bitumens and of asphalt paving mixtures* 



CHAPTER VI. 

CHARACTERIZATION AND CLASSIFICATION OF THE NATIVE 

BITUMENS. 

In a recent article on the " Bitumens of Cuba " the author has 
shown that while there have been numerous attempts to define the 
nature of bitumen, and to characterize and classify the various forms, 
none of them has been satisfactory, and that this has been plainly 
due to the fact that it is only recently that a sufficient number 
of deposits have been studied in their native environment, and 
in the laboratory, by methods which were sufficiently developed 
to reveal anything as to the constitution of the harder forms. For 
example, the fact that hard bitumen in the form of asphalt con- 
sists of cyclic polymethylenes of two or more rings, of the con- 
densation products of such hydrocarbons and of their derivatives, 
and that this form of bitumen is without doubt the result of the 
metamorphism of cyclic petroleums by natural causes has only 
been made apparent within the last few years. 

This lack of data to serve as a basis of comparison and char- 
acterization of species, and as an aid to the close definition of 
what bitumen is, and how its various forms can be differentiated, 
has been largely supplied, as far as the harder forms — maltha, 
asphalt, gilsonite, grahamite, albertite, etc.— are concerned, by 
the examination in the author's laboratory of several hundred 
occurrences of these materials, scattered over the greater portion 
of the United States and Canada, the West Indies, and the northern 
coast of South America. Our knowledge of the nature of various 
forms of petroleum has also been greatly extended by the work 
of C. F. Mabery, C. E. Coates, E. O'Neill, and numerous con- 
tinental chemists, and that of natural gas by F. C. Phillips and 
others. 

There is, of course, a vast field still open for research, but it 

110 



NATIVE BITUMENS. Ill 

is believed that the presentation of the subject here given is based 
on more complete evidence than anything heretofore attempted. 

What is Bitumen? — The most rational way of approaching 
the question appears to be to present the definitions and character- 
ization of this class of materials as a whole, and then of the par- 
ticular forms as they may be differentiated by the available evi- 
dence; that is to say, to put the results which have been reached 
before the reader, and then to show how these have been arrived 
at from the data and evidence available. 

As a beginning, bitumen and pyrobitumen must be defined : 

Native Bitumens and Pyrobitumens. — Native bitumens con- 
sist of a mixture of native hydrocarbons and their derivatives, 
which may be gaseous, liquid, a viscous liquid or solid, but, if 
solid, melting more or less readily on the application of heat, and 
soluble in turpentine, chloroform, bisulphide of carbon, similar 
solvents, and in the malthas or heavy asphaltic oils. Natural 
gas, petroleum, maltha, asphalt, grahamite, gilsonite, ozocerite, 
etc., are bitumens. Coal, lignite, wurtzilite, albertite, so-called 
indurated asphalts, are not bitumens, because they are not soluble 
to any extent in the usual solvents for bitumen, nor do they melt 
at comparatively low temperatures nor dissolve in heavy asphaltic 
oils. These substances, however, on destructive distillation give 
rise to products which are similar to natural bitumens, and they 
have been on this account defined by T. Sterry Hunt as " pyro- 
bitumens/' which differentiates them very plainly from the true 
bitumens. They usually contain oxygen, whereas the true bitu-. 
mens, as a rule, do so to only a limited extent. 

There is, of course, no sharp dividing line between bitumens 
and pyrobitumens, as the former are gradually metamorphosed 
by time and exposure to varied environment into the latter. 

Classifications of Bitumens. — Among the bitumens there are 
such variations in physical attributes and chemical composition 
that they may be differentiated as follows: 
BITUMENS: 

Gas. 

Natural hydrocarbon gases. 
Marsh-gas. 



112 THE MODERN ASPHALT PAVEMENT. 

Petroleum. 
Paraffine-oils. 

Consisting of hydrocarbons and their derivatives, the 
lower members of which belong entirely to the 
parafhne series and have the general formula C n H 2n+2 . 

(1) Those containing C n H 2n+2 hydrocarbons up to 
C 2 sH 58 with but traces of sulphur derivatives : Penn- 
sylvania, West Virginia, Kentucky, Kansas, Colorado, 
etc. 

(2) Those containing C n H 2n+2 hydrocarbons up to 
C11H24 and above that C n H 2n and C n H 2n _ 2 poly- 
methylenes with considerable amounts of sulphur 
derivatives: Ohio, Canada. 

Cyclic Oils. 

Consisting principally of polymethylene hydrocarbons 
of the series C n H 2n , C n H 2 „_2 + C n H 2 n-4, together 
with a certain amount of unsaturated hydrocarbons 
and their derivatives. 

(1) Stable polymethylenes, consisting largely of naph- 
thenes, C n H 2n : Russian oils. 

(2) Less stable polymethylenes together with consider- 
able amounts of unsaturated hydrocarbons and 
their nitrogen and sulphur derivatives, and leaving 
an asphaltic residue on distillation: California. 

Oils of Mixed Composition. 

Semi-asphaltic oils composed largely of stable paraffine 
and polymethylene hydrocarbons not readily attacked 
by sulphuric acid: Texas. 
Maltha. 

Known also as mineral tar, brea, and chapapote. 

Originating from polymethylene petroleums alone. 
Transition products between oil and asphalt. 
Solid Bitumens. 

Consisting largely of paraffine hydrocarbons. 

Ozocerite, hatchettite, etc. 
Consisting of unsaturated cyclic hydrocarbons. 
Terpenes, fossil resins, amber, etc. 



NATIVE BITUMENS. 113 

Derived from or originating in poly methylene petroleums, 
the more volatile components consisting of di- or tricyclic 
saturated hydrocarbons. 
Asphalts. 

Asphalt. Numerous varieties: Trinidad, Venezuela, Cali- 
fornia, Cuba. 
Glance pitch. 
Consisting largely of cyclic hydrocarbons attacked by strong 

sulphuric acid, but which otherwise are stable. 
Manjak. 

Yielding high fixed carbon and a black powder. 
Gilsonite. 

Yielding average fixed carbon and a brown powder, the 
more volatile components resembling sticky oleo resins 
rather than hydrocarbons found in the asphalts. 
Grahamite. 

Consisting of hydrocarbons almost entirely insoluble in 
naphtha and yielding a higher percentage of fixed carbon 
on ignition. Melting with difficulty. 
The grahamites rapidly shade into pyrobitumens. 
PYROBITUMENS: 

Practically insoluble in chloroform or heavy petroleum hydro- 
carbons. 
Derived from petroleum, 
Albertite, with varieties called nigrite, etc. 
Wurtzilite. 

Derived from direct metamorphoses of vegetable growth. 
Anthracite. 
Bituminous coaL 
Lignite. 
Peat (?). 

Of the bitumens, as we have seen, the hard ones and the 
oils enter into the composition of paving cements and 
must be considered individually. 

SUMMARY. 

The author's classification of the native bitumens and those 
of other writers are unfortunately founded on an empirical basis 



114 THE MODERN ASPHALT PAVEMENT. 

to too great a degree to admit of their being satisfactory to every 
one. Such classifications can be regarded as mere steps toward 
a final conclusion which can only be arrived at after years of 
investigation of the subject. The author's classification is pre- 
sented for what it is worth, and there will be no hesitation in 
modifying it in the future in the light of any additional informa- 
tion which may become available which is based on facts and 
not on mere opinion or theory. For a thorough understanding 
of the character of the native bitumens it is advisable that the* 
general reader should acquaint himself with the peculiarities ox 
the different classes which it has been possible to differentiate, 
the one from the other, in order that an intelligent understanding 
may be arrived at of the very variable nature of the bitumens in 
use in the asphalt paving industry. 

The mere minute differences in the various bitumens, upon 
which their differentiation has been based, will be made plain in 
the following pages. 



PART III. 

NATIVE BITUMENS IN USE IN THE PAVING 
INDUSTRY. 



INTRODUCTION. 

In the light of the preceding classification of the native bitumens 
and our knowledge of the various series of hydrocarbons of which 
they are composed the characteristics of the fluxes, the asphalts, 
and other solid native bitumens in use in the paving business 
may now be taken up. 



CHAPTER VII. 

DIFFERENTIATION AND CHARACTERIZATION OF THE NATIVE 

BITUMENS. 

All the native bitumens are such complicated mixtures of 
various hydrocarbons and their derivatives that it is impossible 
to separate them completely into their individual constituents 
and to differentiate and characterize them in this way. Recourse 
must, therefore, be had to the determination of their physical 
properties and to attempts, more or less successful, to separate 
the proximate constituents of which they are made up into various 
classes according to their solubility and behavior towards reagents, 
supplemented by the determination of the amount of fixed carbon 
which they yield on ignition and their ultimate composition. 

Physical Properties. — The physical properties which are of 

value in characterizing the bitumens are: 

115 



116 THE MODERN ASPHALT PAVEMENT. 

SOLID BITUMENS. 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78 F. Original substance, dry 

' ' ' ' ' ' Pure bitumen 

Color of powder or streak 

Lustre 

Structure 

Fracture 

Hardness, original substance 

Odor 

Softens 

Flows 

Consistency, penetration at 78° F 

The chemical characteristics of interest are: 

CHEMICAL CHARACTERISTICS. 

Original substance 

Loss, 212° F., 1 hour 

Dry substance 

Loss, 325° F., 7 hours 

Character of residue 

Consistency, penetration of residue at 78° F 

Loss, 400° F. , 7 hours (fresh sample) 

Character of residue 

Consistency, penetration of residue at 78° F. 

Bitumen soluble in CS 2 , air temperature 

Inorganic or mineral matter 

.Difference 

Malthenes: 

Bitumen soluble in 88° naphtha, air temperature . . , 

This is per cent of total bitumen. 

Per cent of soluble bitumen removed by H 2 S0 4 .... 
Per cent of total bitumen as saturated hydrocarbons. 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen 

Carbenes: 

Bitumen insoluble in carbon tetrachloride, air tem- 
perature 

Bitumen yields on ignition : 

Fixed carbon 

Sulphur 

Ultimate composition 



NATIVE BITUMENS. 117 

FLUXES. 

PHYSICAL PROPERTIES. 

Specific gravity, dried at 212° F., 78° F./78° F 

Flows, cold test 

Color 

Odor 

Under microscope .' 

Flashes, ° F., N. Y. State oil-tester 

Viscosity P.R.R. pipette at — ° F 

CHEMICAL CHARACTERISTICS. 

Original substance 

Loss, 212° F., 1 hour or until dry 

Dry substance 

Loss, 325° F., 7 hours 

Character of residue 

Penetration of residue at 78° F 

Loss, 400° F. , 7 hours (fresh sample) 

Character of residue 

Penetration of residue at 78° F — 

Bitumen soluble in CS 2 , air temperature — 

Inorganic or mineral matter 

Difference 

Bitumen insoluble in 88° naphtha, air temperature, 

pitch » 

Per cent of soluble bitumen removed by H 2 S0 4 .... 

Per cent of total bitumen as saturated hydrocarbons . 

Per cent of solid paraffines 

Fixed carbon 

Ultimate composition 

Specific Gravity. — For the physical characteristics it may be 
said that the specific gravity of the solid bitumens as they are 
originally found in nature will depend very largely upon the per- 
centage of mineral matter which they contain. One like Trinidad 
lake asphalt, containing 37 per cent of mineral matter, will have 
a specific gravity of 1.40, while an extremely pure bitumen, like 
gilsonite, will have a specific gravity of 1.04. 



118 THE MODERN ASPHALT PAVEMENT. 

Where the pure bitumen is extracted from the native material 
the density will not, as a rule, vary very widely. For the asphalts 
it will lie between 1.03 to 1.07. 

Ozocerite is the only solid bitumen which has a specific gravity 
below 1.00, .912, while grahamite, albertite, and glance pitch 
exceed a density of 1.09. 

The density of the residual pitches, at least of those met in 
the paving industry, is usually quite similar to that of the 
bitumens of the native asphalts, not rising above 1.1, unless in 
their preparation they have been carried to a very high tem- 
perature, nor falling below 1.0 if they are at all solid. Some of 
the condensed oils, such as Byerlyte, Pittsburg flux, and blown 
asphaltic oil, have a density below 1.0 and can be recognized by 
the fact that they float on water. 

The specific gravity of the various bitumens is, therefore, of 
some considerable interest. 

A summary of some of the data collected by the author is 
given in the following table: 

Substance. Specific Gravity. 

Trinidad lake refined asphalt 1 . 4000 

" land " " 1.4196 

Bermudez refined asphalt— 1900 1 .0823 

" —1903 1.0575 

Maracaibo refined asphalt 1 . 0667 

Cuban (Bejucal) asphalt 1 . 3050 

Mexico — Tamesi River asphalt (dry) 1 .1180 

" — chapapote asphalt (dry) 1 .0450 

Calif ornia— La Patera 1 . 3808 

—Standard, refined 1.0627 

Utah— gilsonite firsts 1 .0433 

" — " seconds 1 .0457 

Grahamite — Indian Territory, Ten Mile Creek. . 1 . 1 916 

—Colorado, Middle Park 1.1600 

Egyptian glance pitch 1 . 0970 

Manjak 1 .0844 

Ozocerite— Utah . 9123 

Albertite— Nova Scotia 1 .0790 

" —Utah 1 .0990 

" —Cuba 1 .2040 

Wurtzilite— Utah 1 .0556 

Kentucky, Grayson Co. — seepage .9783 



NATIVE BITUMENS. 119 

Substance. Specific Gravity. 

Utah, Soldier Creek — extracted bitumen 1 .2000 

" Grand Co. — extracted bitumen 1 .0370 

"D" grade Calif orina, carefully prepared 1.0622 

"' " " carelessly '"' .... 1.0887 

Asph. O. &Ref. Co.... 1.0770 

Beaumont, Texas, oil asphaltic residue 1 . 0803 

Baku pitch from Russian petroleum 1 . 1098 

Pittsburg flux .9879 

Ventura flux 1 .0199 

Byerlyte, paving 1 .0230 

; ' roofing . 9070 

Hydroline "B" 1 .0043 

Color of Powder or Streak. — Where the solid native bitumens 
are sufficiently hard to permit of their being powdered or to make 
a streak upon porcelain, the color of the powder or streak may 
be of some value in differentiating them. For example, the powder 
of refined Trinidad lake asphalt is of a bluish-black color, whereas 
that of Trinidad land asphalt is distinctly brown. Most of the 
asphalts give a powder of either a dull-black or brownish-black 
color, but gilsonite is distinguished by its extreme brittleness and 
the fact that the powder is of an extremely light-brown color. 

Lustre. — All the native bitumens are lustrous if pure, with 
the exception of ozocerite. The residual pitches are, of course, 
lustrous. In the presence of mineral matter the lustre is more 
or less diminished, depending upon the amount of the latter. 

Structure. — The structure of the native bitumens is in many 
cases very characteristic. To begin with, it is either uniform 
and homogeneous in every part or the reverse. In crude Trinidad 
lake asphalt we note the presence of gas cavities and of emul- 
sified water. In some California asphalts large particles of brec- 
ciated shale are scattered through the native asphalt, which occurs 
in veins. On the other hand, gilsonite is of an extremely uniform 
structure except where the material approaches the vein wall, 
where it at times takes on a columnar structure due to weather- 
ing. Glance pitch and manjak are also of extremely uniform 
structure. The same thing may be said in regard to many refined 
asphalts in which the lack of homogeneity has been removed by- 
melting. The structure of the residual pitches is, of course, quite 



120 THE MODERN ASPHALT PAVEMENT. 

homogeneous, except where they may have been coked to a cer- 
tain degree by excessive heating. 

Fracture. — The fracture of the native solid bitumens in many 
cases is as characteristic as the structure. Almost all grahamites, 
although homogeneous in structure, have a peculiar fracture which 
distinguishes them from all the other solid bitumens. It has 
been described as a hackley or pencilated fracture, which, perhaps,, 
covers it sufficiently. It is an irregular fracture and shows no 
evidence of a purely lustrous surface, as in the fracture of gilsonite. 
The fracture of crude Trinidad asphalt is quite irregular, that of 
gilsonite conchoidal and highly lustrous, while that of many refined 
asphalts is only semi-conchoidal. 

Hardness. — The hardness of the native bitumens in the form 
in which they originally occur may be stated in terms of Mohr's 
scale. Where the pure bitumen is softer than 1 of this scale, it 
may be stated in terms of one of the various penetration machines. 

Odor. — The odor of most of the native bitumens is character- 
istic at ordinary temperatures. The asphalts have in general 
an asphaltic odor, but some of them, such as that from near the 
Gulf of Maracaibo, in Venezuela, are characteristically rank. Gil- 
sonite has scarcely any perceptible odor, while the residual pitches 
have a peculiar oily odor. On heating, stronger odors are com- 
monly developed which are recognizable to one accustomed to 
them, but the nature of which is difficult to describe in print. 

Softening and Flowing Points. — The native bitumens possess 
no melting-point. It can be stated that they are in a melted 
condition at such and such a temperature, but since they are 
made up of a mixture of hydrocarbons and their derivatives it 
is impossible for them to have a true melting-point, such as that 
of ice or any definite compound. In cooling a mass of water in 
which a thermometer is immersed from any temperature, say 50° F., 
to a point below freezing and representing this on a system of 
coordinates, the time being denoted by the abscissae and temper- 
ature by the ordinates, a curve will be developed which at the 
point of freezing, while the water is being converted into ice, is 
broken by a straight line which denotes the time during which 
the liquid is becoming converted to ice. If any native bitumens 



NATIVE BITUMENS. 123 

are melted and cooled in the same way no definite break corre- 
sponding to any definite freezing-point is detected. It is, therefore, 
impossible for us to speak of the melting-point of a bitumen, but 
we may determine in any empirical way the point at which any 
solid bitumen softens and again when it flows, as specified in the 
author's method given in Chapter XXVIII. The determinations 
of this nature given in the following pages were made in this way. 
Chemical Characteristics. — It will be noted that in the differen- 
tiation of the bitumens into classes by means of solvents, certain 
names have been applied to the various classes of hydrocarbons. 
In the early days of the study of the behavior of solvents towards 
native bitumens, the various hydrocarbons and their derivatives 
were differentiated, according to their solubility in naphtha, into 
classes to which the names " Petrolene " and " Asphaltene," 
terms used by Boussingault in his earliest investigations, were 
applied. These terms were open to the objection that it led per- 
sons not thoroughly acquainted with the chemistry of the natural 
hydrocarbons to believe that petrolene and asphaltene were 
definite compounds, which, of course, is no more the case than to 
assume that the oil known under the name kerosene is a definite 
compound. The author, therefore, changed the designation to 
" Petrolenes " and " Asphaltenes " as more plainly indicating 
that the differentiation was merely one of classes. More recently 
it has seemed possible to carry the differentiation still further, 
since it has been found that the solubility of the native bitumens 
in cold carbon tetrachloride is not in all cases the same as in bisul- 
phide of carbon or chloroform and that solubility or insolubility 
in this medium can be added to those previously employed for 
this purpose. Peckham has also shown that chloroform dissolves 
hydrocarbons which are not soluble in carbon disulphide, and 
this solvent may be added to our list, or even oil of turpentine 
if thought necessary. The author's idea in regard to the future 
differentiation of the native bitumens would involve the applica- 
tion of the term " Malthenes," to the bitumens soluble in naphtha 
in place of the term " Petrolenes," stating the specific gravity 
of the naphtha used as a solvent, as this class of bitumens bears a 
great resemblance to the malthas; reserving the term " Petrolenes -5 



122 THE MODERN ASPHALT PAVEMENT. 

for those hydrocarbons which are volatile at 325° F. in 7 hours, 
according to the author's method, these hydrocarbons being com- 
paratively light oils resembling ordinary petroleum. He would 
characterize as " Asphaltenes " those hydrocarbons and then- 
derivatives which are soluble in cold carbon tetrachloride and 
as " Carbenes " those not soluble in cold carbon tetrachloride, 
but soluble in carbon disulphide. This differentiation has not 
been carried out in the author's work to any great extent in the 
past, but in many cases in the following tables the percentage of 
the bitumen insoluble in cold carbon tetrachloride will be found 
to prove of great interest. 

In the determination of the amount of fixed carbon which any 
native bitumen will yield when heated to a high temperature in 
the absence of oxygen, after the manner proposed for making the 
same determination in coal, data are obtained which are of great 
interest as showing the relative proportion of carbon and hydrogen 
in the bitumen under examination. In the case of the parafhne 
hydrocarbons of the formula C n H 2n +2 no fixed carbon is left on 
ignition, while the amount increases with each diminution in the 
proportion of hydrogen to carbon, until in grahamite as much 
as 50 per cent is found, where the relation of carbon to hydrogen 
is as 8 to 1. 

The ultimate composition of the bitumens is, of course, of 
interest, but for general purposes the information derived from 
this determination seldom repays the time and care necessary. 

The methods employed in arriving at the results which are 
presented in the following tables are given in a later chapter of 
this book, and reference must be made to it for the details of the 
process and for a thorough understanding of what each deter- 
mination may mean. 1 

It will be found on examining these methods that the results 
obtained by their use are in no sense absolute determinations, 
but when each of the asphalts is treated in quite the same way 
as the others they are of great value relatively and for purposes 
of comparison and differentiation. In regard to certain of the 
data some explanation will be necessary. 

1 Page 519. 



NATIVE BITUMENS. 123 

Bitumen Soluble in Bisulphide of Carbon, Air Temperature. — This 
determination shows the amount of bitumen which is soluble in cold 
bisulphide of carbon. If hot bisulphide of carbon, chloroform, or 
turpentine and in some exceptional cases hot carbon tetrachloride 
are used as a solvent, a slightly larger percentage would probably be 
found but, owing to the difficulties in maintaining uniform conditions 
for extraction at other than ordinary temperatures and for other 
reasons which it is unnecessary to specify here, cold bisulphide 
of carbon has been used and the results obtained are more satis- 
factory for comparative purposes than would otherwise be the 
case. 

Inorganic Matter. — The determination of inorganic or mineral 
matter represents the residue remaining on the ignition of the 
native bitumen in a muffle at such a temperature as to remove 
all the carbon. In certain cases the amount obtained may be 
less than that originally present, owing to the volatilization of 
alkalies or sulphuric acid, but it is sufficiently accurate for pur- 
poses of comparison. 

Insoluble or Difference. — On adding together the percentages 
of bitumen soluble in carbon disulphide and of inorganic matter 
obtained on ignition, the sum will seldom amount to 100.0. The 
difference which is stated as such in our analyses has for many 
years been considered as organic matter not bitumen. This may 
be true in exceptional cases, but recent investigations 1 have shown 
that it is not at all so in many bitumens. For example, in Trinidad 
asphalt it has been found to consist of the water of combination of 
the clay which the material contains and some inorganic salts which 
are volatilized on ignition. The amount of organic matter is 
extremely small. In other cases, it may consist to a considerable 
extent of grass and twigs, as in the seepages which have run 
out over sod. On the whole, therefore, it seems desirable not to 
describe it by any definite name, but merely as an undetermined 
difference. 



1 Proc. Am. Soc. Test. Mat., 1906, 6, 509. 



124 THE MODERN ASPHALT PAVEMENT. 

Loss at 325° F. in 7 hours. — The hydrocarbons lost at 325° F., 
which the author has proposed to denominate " Petrolenes," as a 
class, will vary in amount enormously according to the conditions 
under which the heating is carried out. When these are accu- 
rately defined, however, as in our methods, the relative loss is 
an important indication in differentiating any two bitumens. 

Malthenes. — It is a well-known fact that the percentage of 
malthenes or bitumen soluble in naphtha will vary according to 
the solvent used, and in the case of naphtha if its density is low, 
according to the method by which the solvent is applied. In 
the determinations given in the table naphthas of a definite density, 
88° and 62° Beaume, have bsen allowed to act on the native bitu- 
men, in as finely a comminuted condition as possible, in the cold 
for a definite length of time and the residue washed quite clean 
with the same solvent. Had the solvent been applied warm or 
in a continuous percolation apparatus the figures would have 
been higher but would not have been constant, since the lighter 
hydrocarbons in the solvent would have been gradually volatilized 
and their solvent power slowly increased. For comparative pur- 
poses the method in use is more satisfactory than any other, but 
the results themselves are of no value as an absolute differentiation 
of the native bitumen into two definite classes of materials. 

Action of Strong Sulphuric Acid on the Hydrocarbons. — The 
results presented showing the action of strong sulphuric acid on 
the hydrocarbons soluble in 88° naphtha are only of value because 
all of them are carried out according to a definite and arbitrary 
method. If this were varied the results would also vary. It is 
important to know that strong sulphuric acid has a somewhat 
different action on the hydrocarbons of a solid bitumen if it is 
allowed to act on an 88° or 62° naphtha solution of them. In 
the 62° naphtha solution the action is apparently much less than 
in the solution of the solvent of lighter density. 

Bitumen Insoluble in Carben Tetrachloride, Air Temperature. — 
The amount of bitumen soluble in cold carbon tetrachloride, in all 
the normal asphalts, is practically the same as that soluble in 
carbon disulphide, but in certain native bitumens hydrocarbons are 



NATIVE BITUMENS. 125 

found which are insoluble in this medium. This differentiates these 
bitumens — grahamite, for example — from the true asphalts, the 
insoluble bitumen forming a class of hydrocarbons or of their 
derivatives to which the name of " Carbenes " has been applied. 
Such bitumens have evidently been much more metamorphosed 
by weathering or otherwise than the true asphalts, or have orig- 
inated in a different series of hydrocarbons. 

In residual pitches, at times some of the bitumen is found 
which is insoluble in cold carbon tetrachloride, and this is evi- 
dently due to the severe treatment which the material has suffered 
in the course of its production at very high temperatures. A 
determination of the amount is only valuable as an indication 
of the care which has been used in the preparation of such pitches. 
In the best asphaltic residues from California petroleum the per- 
centage of " Carbenes " has been found to vary from 7 to less 
than one-half of 1 per cent. 

Fixed Carbon. — The amount of fixed carbon which any solid 
native bitumen will yield will depend, as in the case of coal, upon 
the way in which the material is ignited. All the determina- 
tions given have been made by following the scheme suggested 
by the Committee of the American Chemical Society on the Analysis 
of Coal, and are, therefore, strictly comparable. 

With these facts in view the analyses of the native bitumens 
which are to be presented will be of interest for the purpose of 
comparing the characteristics of the various materials, but the 
chemical data must not be looked upon as being absolute in any 
case. 

SUMMARY. 

By determining the physical characteristics of any native 
bitumen, its specific gravity, its color in a powdered condition, 
its lustre, structure, fracture, hardness, odor, softening point, 
and consistency, by differentiating the bitumen into various classes 
of hydrocarbons by means of solvents and by observing certain 
other chemical characteristics, such as the ultimate composition, 
the amount of fixed carbon left on ignition, and the extent to 
which the hydrocarbons of which it is composed are acted upon 



126 THE MODERN ASPHALT PAVEMENT. 

by strong sulphuric acid, it is quite possible to characterize and 
classify the various native bitumens in such a way as to make it 
possible to recognize them without difficulty and without con- 
fusing one with another. The methods for making these deter- 
minations appear in Chapter XXVIII. 



CHAPTER VIII. 
PETROLEUMS. 

In the asphalt paving industry the petroleums are of interest 
because the heavier hydrocarbons or residuum which remains 
on distilling off the lighter portion of the oil are used as a flux 
for the solid native bitumens. The character of these residuums 
and fluxes reflects, of course, the nature of the petroleum from 
which they have been made, the paraffine oils yielding a residuum 
of one kind, the asphaltic oils one of another, and the mixed par- 
affine and asphaltic oils, such as those from the Beaumont field 
and elsewhere in Texas and from Oklahoma and part of Kansas, 
one of quite another character. 

For a more definite knowledge of the proximate composition 
of various petroleums, beyond that which has been given in the 
classification, reference must be made to the publications of those 
who have devoted their time to a study of this subject, among 
whom may be named Mabery, Young, MarkownikofT, and Engler, 
Unfortunately the publications of these investigators are widely 
^scattered and appear nowhere in condensed form. Their general 
conclusions have been included in the author's classification 
of petroleums. 

Malthas. — The malthas are viscous liquid natural bitumens cor- 
responding in consistency to that of the artificial residuums or usually 
denser. They are only rarely of a suitable character for use as a 
flux, owing to the fact that on heating they are generally rapidly 
converted into a harder material by the loss of volatile hydro- 
carbons and condensation of the molecule. It was due to this 
fact that the early pavements laid with Alcatraz asphalt were 
not successful. The flux in use was a natural maltha derived 
from the Carpinteria sands, which, while of the proper consistency 

127 



128 THE MODERN ASPHALT PAVEMENT 

as prepared, was rapidly converted into a solid bitumen on pro- 
longed heating. 

The bitumen in the Kentucky sands is much more of the nature 
of a maltha than of an asphalt, and it is on this account that these 
materials are unsatisfactory for paving purposes in addition to 
the fact that they contain usually a much too small percentage 
of bitumen. 

For the above reasons the native malthas are rarely used in 
the preparation of asphalt cement and never with successful 
results. 

On page 129 are given some examples of the characteristics of 
malthas from various parts of the world. 

It appears that the malthas may, when dry but not otherwise 
altered, have a specific gravity either less or greater than water. 
They all volatilize a very considerable amount of light oils at 
325° F., and most of them large amounts at 400° F. In the case 
of four out of nine of those cited the residue after heating to only 
325° F. was hard enough to permit a determination of their con- 
sistency with the penetration-machine. Under the same circum- 
stances a paraffine residuum would still remain a flux, as would 
the best asphaltic petroleum residuums. They frequently contain 
notable percentages of the asphaltenes and all become pitch after 
heating to a constant weight at 400° F. 

The Residuums of Petroleums Used as Fluxes in Softening 
the Solid Native Bitumens. — In order to bring the solid native 
bitumens to such a consistency as will make them available for use 
as a paving-cement it is generally necessary to flux them with 
some other softer bitumen. The flux in use for this purpose is 
uniformly a heavy residuum prepared by the removal of the lighter 
portions of petroleum by distillation. These residues naturally 
vary in character in the same way that the petroleums do from 
which they have, been derived, and that the petroleums are 
very variable, depending upon the series of hydrocarbons of which 
they are composed, has already been made evident. The oils from 
which residuums or fluxes are prepared for use in the United States 
are the paraffine petroleums from the Eastern, Ohio, Kentucky, 
Kansas, Oklahoma, and Colorado fields, the asphaltic petro- 



PETROLEUMS. 



129 





Test No. 


Characteristics of Malthas. 


30374. 

California, 

Sunset 
District. 


30116. 

California, 
McKi trick- 
District. 


25129. 

Cuba, 

Hato. 

Nuevo. 


50912. 

Cuba, 
Matanzas. 


Loss, 212° F 


245° F. 

.9867 

7.0% 

* 

28.0% 
40° 

6.7% 


270° *F. 

.9884 

12.4% 
* 

16.1% 
* 


7.76% 

.9445 

5.8% 
38° 

25.5% 
15.7% 


11.0% 
325° F. 


Flash-point 


DRY SUBSTANCE. 

Specific gravity, 78° F./78° F. 

Loss, 325° F., 7 hours 

Penetration of residue at 78°F. 

Loss, 400° F. , 7 hours 

Penetration of residue 

Loss, 325° F: to constant wt. . 

Penetration of residue 

Loss, 400° F. to constant wt . 

Penetration of residue 

Bitumen insoluble in 88° 
naphtha, pitch 


1.C029 

8.9% 
* 

13.2% 
* 

22.8% 

32.1% 
16° 

17.6% 

8.1% 

8.6% 


Bitumen insoluble in 62° 
naphtha, pitch 


Bitumen yields on ignition : 
Fixed carbon . 



Characteristics of Malthas. 



Test No. 



39556. 

Venezuela, 
Peder- 
nales. 



10106. 

Venezuela, 
Mene 
River. 



63846. 

Texas, 
Austin. 



30283. 

Trinidad, 
Boodoo- 
shingh. 



60487. 

Trinidad, 
Mara- 
bella. 



Loss, 212° F. . 

Flash-point 

DRY SUBSTANCE. 

Specific gravity 78° F./78° F 

Loss, 325° F., 7 hours 

Penetration of residue at 78°F. 

Loss, 400° F., 7 hours 

Penetration of residue 

Loss, 325° F. to constant wt. . . 

Penetration of residue 

Loss, 400° F. to constant wt . . 

Penetration of residue 

Bitumen insoluble in 88° 

naphtha, pitch 

Bitumen insoluble in 62° 

naphtha, pitch 

Bitumen yields on ignition : 

Fixed carbon 



9.7% 



1.032 

4.6% 
75° 

11.1% 
23° 



9-0% 



5% 
* 

9% 



4% 



7.0% 



1.5% 



.974 

7.1% 
* 

17.0% 



31.0% 
13° 

3.5% 



18.5% 



10.4% 
hard 



5.2% 



6.4% 
32° 

10.3% 
20° 



40.4% 
25.9% 
10.0% 



* Too large to read. 



130 THE MODERN ASPHALT PAVEMENT. 

leums from California and the petroleum of mixed character 
from Texas containing both paraffine and asphaltic hydrocarbons. 
The residues from paraffine petroleum usually carry a very con- 
siderable amount of paraffine scale, which has a decided influence 
on their character. The residue from Texas petroleum from the 
Beaumont field, now nearly exhausted, contained only a small 
amount of paraffine hydrocarbons and not more than 1 per cent 
of paraffine scale. The supply of flux of this character is now very 
small, and is all produced at Chaison, Texas. The greater part 
of the Texas flux on the market in 1907 was produced from pipe 
line oil from the various Texas and Oklahoma fields. This petro- 
leum is necessarily of a very mixed character and the flux pre- 
pared from it has contained very considerable amounts of paraffine 
hydrocarbons and scale, the latter reaching at times as high 
as six per cent. It is far less satisfactory as an asphaltic flux than 
that prepared from the original Beaumont oil, and in some respects 
is not a suitable substitute for it. For use with ordinary asphalts 
it is, however, as good for paving purposes, although perhaps 
not quite as stable at high temperatures. It must be used as a 
paraffine flux. The California residuum or flux is composed 
almost entirely of complicated polymethylenes and contains notable 
proportions of aromatic hydrocarbons, nitrogenous bases, and 
phenols, and is characterized by its very great density. 

Residuums from the same kind of petroleum may, on the 
other hand, vary very largely among themselves, according to 
the care with which they have been prepared. It is quite as 
necessary, therefore, to determine whether a flux has been care- 
fully distilled as it is to know the character of the petroleum from 
which it has been produced. 

In making a comparative study of the available fluxes it will 
also be necessary to determine whether there is a preference in 
favor of one over another as an actual solvent for the solid bitu- 
mens, and to determine their stability and such other properties 
as may point to their adaptability for use in the preparation of 
an asphalt cement. 

The fluxes now in use in the paving industry may be con- 
sidered as consisting of the three classes which have been men- 



PETROLEUMS. 



131 



tioned above, and their character may be taken up according to 
such a classification. 

Paraffine Petroleum Residuum. — Paraffine petroleum residuum 
is the form of flux originally used in the asphalt paving industry 
in the United States. It is also known as petroleum tar and was 
originally a by-product remaining after the distillation of crude 
Pennsylvania paraffine petroleum for the production of illumi- 
nating-oil. It was the flux used by De Smedt in the early days 
of the paving industry for imparting a proper consistency to Trini- 
dad asphalt in the production of paving-cement. Its use has 
been largely continued up to the present time, but its character 
has been greatly modified and improved. It is no longer a by- 
product, but is especially prepared for the purpose. 

In the early days of the industry the residuum used in the 
preparation of asphalt cement was of most varied character. 
Among available records it is found that in the summer of 1888 
several residuums in use had the following properties : 



Flash. 




Gravity. 


230° F. 


22° B. 


.9240 


203° 


24° 


.9130 


226° 


25° 


.9070 


392° 


27° 


.8950 


428° 


22° 


.9240 


176° 







The result of making a cement with oil flashing at 176° F. 
would be that much of it would be easily volatilized at the tem- 
perature of melted asphalt cement, 325° F. ; and that the con- 
sistency would of course be most unstable. 

In 1889 the oils in use had the following characteristics: 



Source. 


Gravity. 


Flash. 


Volatile, 400° F. 


Eagle Refining Co 


22.8° B. 

21.7° 

20.8° 


416° F. 

361° 

271° 


14.40% 
14.33 


Maloney Oil Co 


Jenney Mfg Co 


16.80 







132 THE MODERN ASPHALT PAVEMENT. 

As late as 1892 the oils were still variable: 



Source. 

Solar 

Jenney 

National 

Whiting 

Continental (Denver) 
Crew Levick 



Gravity. 



Flash. 



Volatile, 400° F. 



21.0° B. 

18.5° 
20.0° 
22.2° 
23.8° 
20.4° 



41 7 C 
235 c 
295 c 
415 c 
345 c 
320 c 



4.06% 
11.20 
15.94 

5.39 
15.73 
17.36 



In 1891 the Standard Oil Company undertook to prepare a 
heavy oil especially for paving purposes which should be fur- 
nished to those who were particular as to its character and were 
willing to pay for a better quality. It has had the following 
average composition since 1896: 



PARAFFINE RESIDUUMS. AVERAGE AND EXTREMES IN 
COMPOSITION FOR FOUR YEARS. 



Year.' 


Volatile, 
400° F. 


Extremes. 


Specific 
Gravity. 


Extremes. 


Flash. 


Extremes. 


1896 
1897 
1898 
1899 


4.7% 
6.1 
5.1 
3.8 


2.6- 8.8 
1.4-12.3 
2.9- 8.8 
2.0- 6.4 


.9313 
.9302 
.9327 
.9331 


.9204-. 9351 
.9219-. 9383 
.9206-. 9397 
.9295-. 9376 


430° F. 

420° 
432° 
442° 


397°-476° 
393°-456° 
392°-455° 
416°-460° 



Consistency after heating : Flows slowly at about 78° F. 

The great uniformity of the supply is apparent. Oil of the 
old character is still in use by careless contractors, as it is cheap. 
Oils of this description which have come under my observation 
have the following characteristics: 



Specific 
Gravity. 


Flash. 


Volatile, 
400° F., 7 Hours. 


.9100 
.9197 
.8829 
.9222 


280° F. 
330° 
2C0° 
286° 


23.9% 
17.3 
27.2 
12.6 



The best paraffine residuum from Ohio petroleum and some of 
the Kansas and Colorado fields, which has been in use during the 



PETROLEUMS. 



133 



past six or seven years has commended itself in quality from the 
fact that it is carefully prepared for the paving industry by dis- 
tillation with steam agitation without cracking— that is to say, 
decomposition of the oil— that it has a high flash point, and on 
this account contains little oil volatile at the temperatures at 
which asphalt cement is maintained in a melted condition, and 
that it is uniform. The possible disadvantages of such dense 
residuum, if they are such, in comparison with the lighter and 
more volatile oils are, that more of this oil must be used to pro- 
duce a cement of given penetration or consistency and that at 
comparatively low temperature asphalt cements made with it 
harden more than when lighter oils are used, owing to the separa- 
tion of paraffine scale. 

The only advantage of the lighter form of residuum, how- 
ever, is the one just mentioned, that it and the cement prepared 
from it do not harden or solidify as much in winter tempera- 
tures. 

Typical Paraffine Fluxes of 1907. — In the following table are 
given the characteristics of various paraffine fluxes which were 
available and in use in the paving industry in the year 1907. 
Many of the paraffine fluxes, analyses of which were given in the 
original edition of this work, are no longer available, and there is 
no assurance that the supply for any one year can be duplicated 
the following one. 



Character of flux 

Manufacturer 

Date shipment received 

Test number „ 

Sp. gr.— Beaume— at 78° F. 

Sp. gr.— actual— at 78° F 

Flash point, degrees F. 

Volatile 7 hours, at 212° F 

Volatile in 7 hours, 325° F. (dry sample) 
Residue at 78° F 

Bit. insol. 88° naphtha, pitch 

Per cent sol. bit. rem. by H 2 S0 4 

Paraffine scale 

Fixed carbon 



Paraffine 
Solar Ref 
Lima, Ohio 

10-28-07 
100537 

18.4 
. 943 
455 

•1% 
.2 
Crystalline 
Slow flow 
2.7 
24.9 
6.4 
2.8 



Paraffine 
S. O. Co. 
Whiting, 

Ind. 

10-30-07 

100610 

20.5 
.930 
425 

.2% 

1.2 

Crystalline 

Quick flow 

3.4 

24.7 

7.9 

1.9 



Paraffine 

S. O. Co. 

Neodesha, 

Kan. 

11-10-07 

100446 

21.2 
.926 
435 
.4% 
.6 
Crystalline 
Quick flow 
2.6 
25.9 
8.9 
1.8 



134 



THE MODERN ASPHALT PAVEMENT. 



The petroleum residuum used in the work carried out under the 
author's supervision is furnished under the following specifications: 

Specifications for Paraffine Flux, 1907-1908. — "This oil or flux 
shall consist of the heavier or higher boiling portions of any par- 
affine petroleum. It shall have a specific gravity of between .942 
and .924 (18.6-21.5° B.) at 78° F. 

"It shall be free from water and decomposition products, shall 
contain not more than 2% of bitumen insoluble in 88° naphtha 
not more than 10% of material recovered when one gram of the 
flux is treated as for the determination of paraffine scale, accord- 
ing to the method described in "The Modern Asphalt Pavement," 
John Wiley & Sons, and shall not volatilize more than 5% at 
325° F. in 7 hours." 

It appears from the preceding table and from our specifications 
that a residuum from a paraffine petroleum, such as used in the 
asphalt industry at the present day, if it is in the highest degree 
desirable, should have a specific gravity of .93, equivalent to a 
density of 21.0° B., a flash point of 400° F., should volatilize but 
a small amount at 325° F. under certain conditions which are im- 
posed, should be practically completely soluble in carbon disul- 
phide, and to the extent of 95 per cent in 88° naphtha. The par- 
affine scale should be less than 10 per cent, and the amount of 
fixed carbon which is obtained on ignition not over 4 per cent. 

It will be noted in the preceding analyses that the percentage 
of paraffine scale varies, in the samples examined, from 6.4 to 
8.9 per cent. In other residuums even more paraffine scale has 
been found, as can be seen from the following determinations 
which were made some years ago in the author's laboratoi v. 



Manufacturer. 


Paraffine . 


Craig Oil Co., Milwaukee 


17.6% 
8.7 

12.3 

7.1 

14.5 

33.3 

9.1 


Crew Levick Co., Philadelphia 

American Petroleum Product Co., Find- 
lay, Ohio 


Scofield, Shurmer & Teagle, Indianapo- 


Standard Oil Co 


Wilburine Oil Co., Brooklyn 


Standard Oil Co., thin oil 





PETROLEUMS. 135 

The smaller the amount of paraffine scale that is present the 
more desirable the flux, since a substance of this nature which 
becomes solid at low temperatures cannot be advantageous in a 
paving cement. That paraffine residuum is an extremely stable 
oil appears from the fact that about 75 per cent of the hydrocar- 
bons of which it is composed are not attacked in 88° naphtha 
solution by concentrated sulphuric acid, a fact which is confirmed 
by exposing such a residuum to water for many years, when no 
action is found to have taken place. 1 

The characteristics of asphalt cement made with paraffine 
residuums of various densities, and the refutation of the claim 
that it is not a satisfactory solvent for asphalts and is unsuited 
for the purpose for which it is used in the paving industry, will 
be taken up later when asphalt cements are under consideration. 
It is merely necessary to state here that of such a residuum as 
has been described from 18 to 22 pounds must be used with every 
100 pounds of refined Trinidad lake asphalt in order to produce 
a cement of proper consistency for paving purposes. 

Kansas Petroleum Residuum. — Within the last two years 
a flux has appeared on the market which is prepared from the oils 
coming from the Kansas fields through pipe lines to the East. 
This flux is very peculiar in character. It possesses largely the 
characteristics of a paraffine, and some of those of an asphaltic 
flux. It is peculiar in that, although it carries but 6.7% of par- 
affine scale, it leaves a solid, cheesy residuum amounting to 85% 
of the original oil on heating at 400° F., while, on being main- 
tained at that temperature for a considerable period of time, it 
decomposes with the separation of a granular insoluble material, 
and with the evolution of gas. On this account it is looked 
upon by the author as more or less unsuitable. It has been used 
to a very large extent, however, and apparently works satis- 
factorily at ordinary temperatures with Trinidad and Bermudez 
asphalt. It is to-day one of the largest sources of supply of flux 

1 Whipple & Jackson, The Action of Water on Asphalt. Engineering 
Record, March 17, 1900, 41. 



136 THE MODERN ASPHALT PAVEMENT. 

in the paving industry and its value can only be shown by service 
tests. hi the meantime, it must be classed as a paraffine 
residuum. 

Its characteristics are shown in the following table: 



Manufacturer Standard Oil Company, 

Brooklyn, N. Y. 

Received from Maurer, N. J. 

Date shipment received , 5-10-08 

Test number 2857-M. 

Specific gravity— Beaum^— at 78° F 19.4° 

Specific gravity— Actual— at 78° F .937 

Flash point, degrees F 485 

Volatile in 7 hours at 212° F .2% 

Volatile in 7 hours at 325° F. (dry sample) .6% 

Residue at 78° F Medium slow flow — crys- 
talline 

Volatile in 7 hours at 400° F. (dry sample) 2.0% 

Residue at 78° F Medium flow — crystalline 

Bitumen insoluble in 88° naphtha, pitch 2.7% 

Per cent soluble bitumen removed by H 2 S0 4 23 .4 

Paraffine scale 2.5 

Fixed carbon 3.5 



California Asphaltic Petroleum Residuum. — The petroleums 
of California are characterized by the fact that the residue left on 
distillation, if the latter is carried sufficiently far, is a solid bitu- 
men resembling asphalt. The oil is said, on this account, to have 
an asphaltic base. If the distillation is suspended at a point 
where the residue does not solidify on cooling but remains liquid, 
like a heavy and dense natural maltha, the material known as 
California flux is obtained which has been in use in the paving 
industry to a very considerable extent on the Pacific Coast and 
to but a small extent elsewhere. Such residuums, as found on 
the market in 1907, have the characteristics given in the table on 
page 137. 

Before discussing the characteristics of these residuums it will 



PETROLEUMS. 



137 



be necessary to consider what takes place in the process of their 
manufacture. The petroleum is distilled in cylindrical stills in 
the usual manner with some steam agitation, the temperature 
being eventually carried up to about 600° F. or higher, and main- 
tained there until a sample is slightly heavier than water when 
poured into it. It is very evident that in this process the petro- 
leum is subjected to a very severe treatment and it is not diffi- 
cult to determine at the plant where such flux is produced that 
very decided cracking goes on. That such cracking takes place 
can also be shown by heating a small portion of the original petro- 



CALIFORNIA ASPHALTIC PETROLEUM RESIDUUM. 



Test number. 
Trade name. 



PHYSICAL PROPERTIES. 

Specific gravity, dried at 212° F., 78° F./78° F.. 
Flashes, ° F., N. Y. State oil-tester 



CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 

Character of residue 

Penetration of residue at 78° F. . . . , 



Loss, 400° F., 7 hours (fresh sample). 

Character of residue 

Penetration of residue at 78° F 



Bitumen soluble in CS^, air temperature. 

Difference 

Inorganic or mineral matter 



Bitumen insoluble in 88° naphtha, air temper- 
ature, pitch 

Per cent of soluble bitumen removed by H 2 S0 4 . 

Per cent of total bitumen as saturated hydrocar- 
bons 



Per cent of solid paraffines. 
Fixed carbon 



68489 
"No. 2" 


69607 
"G" grade 


1.002 
354° F. 


1.006 » 
376° F.» 


5.9% 
smooth 

soft 


3.2% » 
smooth 
soft 


16.7% 

smooth 

soft 


17.3% 

smooth 

soft 


99.9% 
.1 
.0 


99.7% 
.3 
.0 


100.0 


100.0 


7.6% 
48.3 


7.7% 
54.9 


47.9 


41.9 


.0 


.0 


6.0 


6.0 


3 Extremes 


5.50-.83. 



1 Extremes 1.018-.993 



2 Extremes 430°-350°. 



leum in a glass dish in an oven at not over 400° F., when the lighter 
portions all volatilize without cracking and the residue recovered 



138 THE MODERN ASPHALT PAVEMENT. 

is found to be of the same consistency but much larger in amount 
than that obtained by the industrial process. It is further not, 
moreover, surprising that cracking should take place very readily 
with California petroleums, since it is known that they are com- 
posed of the unstable polycyclic polymethyienes of a high degree 
of molecular aggregation. 1 

In California flux, therefore, we have one which is of a much 
greater density than that derived from paraffine petroleum, or 
even that derived from Beaumont, Texas, asphaltic oil. It origi- 
nates in an unstable petroleum and has been subjected to very 
severe treatment, and is, therefore, partially cracked. This is 
apparent in some of the determinations given in the preceding 
table, where the amount of oils volatile in seven hours at 400° F. 
is found to be much larger than would be the case with a stand- 
ard paraffine residuum under similar treatment. This loss, about 
17 per cent, must be due to the volatilization of light oils produced 
by cracking. 

Of the components of these California fluxes only 40 to 50 per 
cent consist of saturated hydrocarbons as compared to 70 or 80 per 
cent found in paraffine residuum. This points with great prob- 
ability to the conclusion that such fluxes will harden with age 
and exposure much more rapidly than the more stable paraffine 
fluxes. 

It will be noted that the residue after heating the California 
flux to 400° F. is still soft. This is a property which is abso- 
lutely essential and differentiates these fluxes from the natural 
malthas, which, as has appeared, usually become converted into 
hard pitches on heating for any length of time to a high tem- 
perature, and it is this property which makes it possible to use 
the modern California residuums as a flux. 

The fixed carbon which the California residuums yield on 
ignition is larger than that found in the paraffine residuum, as 
would be expected from the character of the hydrocarbons of 
which it is composed, those in the California oil containing a 

1 J. Soc. Chem. Ind., 1900, 19, 123. 



PETROLEUMS. 139 

very considerably larger percentage of carbon than those found in 
the eastern residuums. 

In drawing specifications for a California asphaltic flux it 
should be provided that it should remain soft after heating for 
seven hours at 400° F. The specifications which the author has 
proposed for use in work under his directions on the Pacific slope 
are as follows: 

Specifications for " G " Grade California Flux. — " California 
flux, known as ' G ' Grade Flux, should be a residue from the 
distillation of California petroleum, with steam agitation, at a 
temperature not above 620° F. 

" It shall have the following characteristics: 

" It shall be soluble in carbon disulphide to the extent of 99 
per cent and in 88° naphtha to the extent of 90 per cent. 

" It shall be free from water, shall not flash below 350° F. 
in a New York State oil-tester, and shall have a density of not 
less than .98, 12.9° B., or more than 1.050, 9.3° B., at 25° C. when 
referred to water at the same temperature. 

" It shall volatilize not more than 5 per cent of oil when heated 
for seven hours at 325° F., according to the method employed in 
the New York Testing Laboratory. 

" The residue from heating the oil in the same way to 400° F. 
for seven hours shall be a soft flux not hard enough to give a pen- 
etration of less than 150° with the Bowen penetration machine. 

" It shall not yield more than 6 per cent of fixed carbon on igni- 
tion. Under the microscope, beneath a cover-glass, it shall appear 
free from insoluble or suspended matter." 

One of the most important characteristics of a California flux 
to be noted from an industrial point of view is that, owing to 
its great density, more than twice as much of it is required to 
soften the solid native bitumens as of a parafnne residuum 
or of one of the semi-asphaltic nature produced from Texas oil. 
For example, with Trinidad asphalt 51 pounds of a California 
flux are often necessary to make a cement of normal penetration 
where no more than 22 pounds of parafnne residuum are used. 

The disadvantages to be met with in the use of a California 
flux or the defects in its character have been presented in the 



140 THE MODERN ASPHALT PAVEMENT. 

preceding paragraphs. Aside from this the flux presents certain 
advantages and desirable properties which cannot be equalled 
in any other softening agent, and on this account makes it of 
great value in certain problems in the paving industry. With 
an asphalt such as that from La Patera, California, or the Bejucal 
mine in Cuba, a satisfactory paving material could not be made 
were it not possible to supply the deficiencies of malthenes in 
these hard bitumens by means of those present in a California 
flux. The use of the material in this way was well illustrated 
in the Alcatraz XX asphalt, which was formerly on the market. 
Sixty per cent of La Patera asphalt was mixed with 40 per cent of 
dense California residuum and the resulting product was a bitumen 
which contained asphaltenes and malthenes in normal propor- 
tions, and which, when made with care and uniformity, proved a 
desirable material. Great uniformity in its manufacture was not 
possible, however, and the defects inherent therein will be consid- 
ered when the study of asphalt cements is taken up. 

As in the case of parafrine residuums, so with the California 
fluxes : in the early days of the industry they were not at all care- 
fully prepared, and even to-day many of them are found on the 
market which are too badly cracked to be desirable. They can, 
with care, however, be prepared with a very considerable degree 
of uniformity, as can be seen from the extremes given in the table 
on page 137. 

As an example of an unsatisfactory flux the following will 
serve: 

TEST NO. 69012. 

Specific gravity, 78° F./78° F 9815 

Loss, 212° F 8% 

" 325° F., 7 hours 8.0 

" 400° F. " " (fresh sample) 16.2 

Penetration of 400° F. residue 43° 

Bitumen insoluble in 88° naphtha, air temp. 9.0% 
Fixed carbon 6.0 

In this flux the specific gravity is low, with the result that 
there is a large loss of volatile matter at 325° F.,. while the residue 
after heating to 400° F. is a solid bitumen, showing that the flux 
is not a stable one and therefore undesirable. 



PETROLEUMS. 



141 



Fluxes from Beaumont and Similar Oils. — Petroleum of the 
character of that found in the well-known Beaumont field in 
Texas is usually considered to have an asphaltic base, but, as is 
not so well known, it also contains a very considerable propor- 
tion of paraffine hydrocarbons, or hydrocarbons which are ex- 
tremely stable, as shown by their behavior with sulphuric acid, 1 
the loss on treatment of the crude oil with sulphuric acid being 
only 39 per cent as compared with 30 per cent for an Ohio oil 
and a still larger amount for the asphaltic petroleums of Cali- 
fornia. The result is that the residuum or flux prepared from 
Beaumont petroleum possesses some very desirable properties, as 
revealed by the following determinations: 



BEAUMONT, TEXAS, FLUX. 



Test number 

Quality 

PHYSICAL PROPERTIES. 

Specific gravity, dried at 212° F., 78° F./78° F. 
Flashes, ° F., N. Y. State oil-tester 

CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 

Character of residue 

Penetration of residue at 78° F 

Loss, 400° F., 7 hours (fresh sample) 

Character of residue 

Penetration of residue at 78° F 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Bitumen insoluble in 88° naphtha, air temper 
ature, pitch 

Per cent of soluble bitumen removed by H 2 S0 4 . 

Per cent of total bitumen as saturated hydrocar 
bons 

Per cent of solid paramnes 

Fixed carbon 



69330 
light 


66364 
heavy 


.9565 
395° F 


.9735 
418° F. 


4.3% 

smooth 

soft 


•8% 
smooth 
soft 


14.5% 

smooth 

soft 


6.2% 

smooth 

soft 


99.8% 
.2 
.0 


99.6% 
.4 
.0 


100.0 


100.0 


2.5% 
25.4 


4.8% 
20.9 


72.8 


79.4 


1.0 


1.7 


3.0 


3.5 



1 J. Soc. Chem. Ind., 1901, 20, 690. 



142 THE MODERN ASPHALT PAVEMENT. 

When the preceding results are compared with those which 
have been given as representing the character of the paraffine 
residuums and of California fluxes, it will be seen that the density 
of these oils is much higher than that of the true paraffine residuums, 
but much lower than that of the California fluxes, and that the 
percentage of total bitumen which is present as saturated hydro- 
carbons is between 70 and 80 per cent as compared to 40 and 
50 per cent in the latter form of flux. This must be a very desir- 
able property and one which is due probably to the presence 
of an appreciable amount of paraffine hydrocarbons and of a 
large proportion of stable poly methylenes. The investigations 
of Mabery and the author have shown that the polymethylenes 
belong to the C ra H 2n , C n H 2n _2, and C n H 2n _4 series. That par- 
affine hydrocarbons are present, and that some of them are of 
high molecular weight, is revealed by the fact that the residuum 
contains 1 per cent of paraffine scale. As prepared for use as a 
flux the residuum is much denser than ordinary paraffine flux, 
its specific gravity being .95 to .96 as compared with .93 for the 
latter. In other respects, when very carefully prepared, it is not 
essentially different in its physical properties. It sometimes con- 
tains a slightly larger proportion of light oils, volatile at 325° F., 
but the same proportions of the lighter flux and hard asphalt 
are necessary as in the case of paraffine residuum. The denser 
form, with a gravity of .97, is only used with asphalts that are 
deficient in malthenes, such as Trinidad land asphalt. 

The above conclusions only hold true when the residuum is 
carefully prepared and some is found on the market which, 
like the less carefully distilled paraffine residuum of the earlier 
years of the industry, is not satisfactory. If carefully prepared, 
however, it is without doubt the most desirable flux which is 
available to-day for the purpose for which it is used. 

Specifications for this residuum may read as follows: 

"This oil or flux shall consist of the heavier or higher boil- 
ing hydrocarbons of Texas oil containing not more than 3 per 
cent of paraffine scale, as determined according to the method 
described in "The Modern Asphalt Pavement," John Wiley 
& Sons. It shall be of a character suitable for fluxing 



PETROLEUMS. 143 

grahamite and other hard bitumens in such a way that, when 
forty (40) parts of grahamite and sixty (60) parts of the flux are 
melted together at 400° F., the resulting product shall not, after 
24 hours in an ice box, contain free oil or have a granular or short 
structure, due to the presence of paraffine. It shall have a gravity 
not less than .97 at 78° F., shall not volatilize more than five per 
cent when heated at 400° F. for seven (7) hours, and shall not 
flash below 400° F. in a closed oil tester, New York State pattern. 

" It shall be free from water and decomposition products, con- 
tain not more than 3% of bitumen insoluble in 88° naphtha, 
and shall not volatilize more than 5 per cent when heated for 
seven (7) hours at a temperature of 325° F." 

As has already been said, the supply of flux of this description 
is nearly exhausted at the present time, owing to the decline of 
the Beafumont field and the mixing of petroleums from various 
fields in pipe lines, many of which contain a large proportion of 
paraffine oil. 

Other Fluxes. — While the fluxes which have been previously 
described are those which are actually in use in the industry in 
the United States, others are found on the Continent of Europe 
which, although not available for use in this country, would be 
entirely satisfactory if this were the case. Among these may 
be mentioned residuum from the distillation of Russian petroleum. 
This is free from paraffine scale and consists of very stable hydro- 
carbons, and with it an especially desirable asphalt cement could 
be made, if it were reduced to a proper density and uniformity. 

In France residuum from the distillation of shale oils is avail- 
able and is largely used in the fluxing of asphalts for use in mastic. 
Such an oil has the properties shown in table on page 144. 

It will be noticed that this oil consists very largely of unstable 
hydrocarbons, as would be expected in one which is the product 
of the distillation of shales, a process in which cracking must go 
on to a certain extent, and contains a very considerable quantity 
of paraffine scale. 

Wax Tailings. — Wax tailings, or still wax, is a thick, yellow- 
brown buttery product at ordinary temperature, which melts 
to a thin liquid at about 175° F. It is the product of the destruc- 



144 



THE MODERN ASPHALT PAVEMENT. 



SHALE-OIL RESIDUUM FROM FRANCE. GOUDRON DE 
SCHISTE D'AUTUN. 



Test number 


65402 

.9849 
215° F 

7.6% 
soft 

26.4% 
soft 

99.7% 
.3 
.0 


72630 


PHYSICAL PROPERTIES 

Specific gravity, dried at 212° F., 78° F./78° F. . 
Flashes, ° F , N. Y. State oil-tester 


.9894 
355° F„ 


CHEMICAL CHARACTERISTICS. 

Dry substance : * 

Loss, 325° F., 7 hours 


5.0% 
soft 


Character of residue. 


Loss, 400° F. , 7 hours (fresh sample) 


10.0% 

soft 


Character of residue 


Bitumen soluble in CS 2 , air temperature. 
Difference 




99.8% 
.2 




Inorganic or mineral matter 


trace 




;emper- 




Bitumen insoluble in 88° naphtha, air 1 
ature, pitch 


100.0 

6.4% 
53.5 

43.6 
4.4 
3.0 


100.0 

7.3% 
58.2 

43.5 


Per cent of soluble bitumen removed by 

Per cent of total bitumen as saturated 

carbons 


H 2 S0 4 . . 
hydro- 


Per cent of solid parafnne 


5.2 


Fixed carbon 


5.0 







tive distillation of paraffine petroleum residuum, the residue in 
the still being coked. 

Owing to the method of preparation the product found on 
the market is extremely variable in character. The results of the 
examination of several lots in the author's laboratory are given 
in the table on p. 145. 

It appears from the data given that, as has been said, 
wax tailings are extremely variable in character. They often 
carry a large amount of water and vary in specific gravity and 
flash point. Usually they contain but little volatile oil, although 
on heating at 400° F. they become converted, as a rule, into a 
solid substance of various degrees of consistency. Wax tailings 
are almost absolutely pure bitumen, and it is surprising to find 
that, although they are the result of destructive distillation they 



PETROLEUMS. 
WAX TAILINGS. 



145 



Test number. 



Original material: 

Loss, 212° F., until dry. . 

" 325° F., 7 hours.... 

Residue— pen. at 78° F . . 



Dry material: 

Specific gravity 78° F./ 

78° F 

Flashes, ° F 



Lo',s,?25°F.,7hours. . . 
Resiaue — pen at78°F. 

Loss, 4C0° F. , 7 hours (fresh 

sample) 

Residue. — pen. at 78° F 



B ; iumen soluble in CS 2 . . . . 

"'yiff^rence 

It '.rgnnic or mineral matter. 



Bitumen sol. in 88° naphtha 
This is per cent of total bitu- 
men 



Bitumen sol. in G2° naphtha 
This is per cent of total bitu- 
men 



>° naphtha sol. bitumen: 
Per cent not removed by 
H 2 S0 4 



Unacted on by H 2 S0 4 ,S0 3 . . . 

Paraf^ne scale 

Fixed carbon 

Bitumen insoluble in cold 
carbon tetrachloride 



30245 

7.0% 



1.02 
298° F. 

5.9% 
83° 



13.3% 
brittle 

99.9% : 



83.1% 



3.7% 



5.5 



55285 



16. 2% l 

58° 



1.0794 
240° F. 



64439 



97.2% 



49.3% 
0.4 



64587 



1.1445 
340° F. 

3.0% 
58° 



4.8% 
9° 

99.8% 
.2 
.0 



100.0 
96.7% 
96.9 
98.9% 
99.1 

50.0% 
1.1 
4.1 
0.0 



64916 
15.5%' 



1.0994 
410° F. 

2.1% 
soft 



4-6% 
50° 

99.8% 
.2 
.0 

100.0 

98.1% 

98.4 

99.6% 

99.7 

55.0% 
2.3 
3.4 
0.0 



Contains a large amount of water. 



2 Unacted on by H 2 S0 4 , 79.9%. 



contain 50 per cent of saturated hydrocarbons unacted upon by 
strong sulphuric acid, although fuming sulphuric acid destroys 
them entirely. Although produced from a residuum carrying 
considerable paraffine scale, mere traces of this material are found 
in the tailings. The amount of fixed carbon which they yield 



146 THE MODERN ASPHALT PAVEMENT. 

is low, as would be expected in the case of a substance derived 
from paraffine petroleum. Wax tailings, owing to the lack of 
uniformity in the material, are of no interest in the paving indus- 
try, but are used to a very considerable extent in insulating and 
other bituminous compounds. 

SUMMARY. 

From the preceding data it appears that there are three 
classes of fluxes available commercially in the United States for 
the softening of native solid bitumens in the preparation of 
asphalt cement for paving purposes: paraffine residuums, as- 
phaltic residuums of California, and the semi-asphaltic residuums 
of Texas, and from the Oklahoma and Kansas fields, the Texas 
being the most desirable of all and probably sufficiently superior 
to the good paraffine residuums to justify an additional expendi- 
ture for its use in work of the highest grade, the reasons for which 
have appeared in the preceding pages. 

The standard residuums from paraffine oil will, however, con- 
tinue to be used over a large area of country where they can be 
obtained at considerably lower prices than other fluxes and where 
the conditions to be met are such that they are entirely satisfac- 
tory. 



CHAPTER IX. 
THE SOLID BITUMENS. 

With the solid bitumens, consisting largely of paramne hydro- 
carbons, such as ozocerite, hatchettite, etc., the paving industry 
has nothing to do, nor is it interested in the terpenes, fossil resins, 
amber, etc., which are composed largely of unsaturated cyclic 
compounds. Our attention must be at once turned, therefore, 
to the solid bitumens which are of commercial importance in the 
paving industry, especially the asphalts. 

The Asphalts. — The asphalts industrially include all the solid 
native bitumens which are in use in the paving and other industries. 
Specifically, true asphalt is sharply differentiated from several of 
the bitumens which are used under this designation, such as 
gilsonite and grahamite. In the table which follows the physical 
properties and proximate composition of the more prominent 
asphalts, using the term in its industrial sense, which are or have 
been used in the paving industry, are given. 

Until recently but little has been known of the nature of 
asphalt beyond the fact that it is a native bitumen. Boussingault's 
investigation of the viscid bitumen and asphalt of Pechelbron, so 
often quoted, threw no light on the question from the point of view 
of modern chemistry, as he merely separated the material into two 
portions, one more volatile than the other, and both, without 
doubt, more or less decomposed by the heat to which they were 
subjected, and consisting of mixtures of various hydrocarbons and 
their derivatives. Warren, who revised the subject of the hydro- 
carbons for Dana's Mineralogy, states that the following " classes 
of ingredients " are present in asphalt (see page 150) : 

147 



148 



THE MODERN ASPHALT PAVEMENT. 

PHYSICAL PROPERTIES AND PROXIMATE 



Test number. 
Bitumen. . . . 



PHYSICAL PROPERTIES. 

Original sub- 



Specific gravity, 78° F./78° F 

stance, dry 

Color of powder or streak. . . 

Lustre 

Structure 

Fracture 



Hardness, original substance. 
Odor 



Softens 

Flows 

Penetration at 78 c 



CHEMICAL CHARACTERISTICS. 



Dry substance: 

Loss, 325° F., 7 hours. 
Character of residue. . 



Loss, 400° F., 7 hours (fresh sample) 
Character of residue 



Bitumen soluble in CS 2 , air temperature. 

Inorganic or mineral matter 

Difference 



Malthenes: 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 
H 2 S0 4 

Per cent of total bitumen as saturated hy- 
drocarbons 



Bitumen soluble in 62° naphtha. 
This is per cent of total bitumen. 



Carbenes : 

Bitumen insoluble in carbon tetrachloride, 
air temperature 

Bitumen more soluble in carbon tetra- 
chloride, air temperature. 



Bitumen yields on ignition: 
Fixed carbon 



Sulphur. 



63260 

Trinidad lake 

refined. 



1.40 

Blue black 

Dull 

Homogeneous 

Semi- 

conchoidal 

2 

Asphaltic 

180° F. 

190° F. 

7° 



1.1% 
Smooth 

4.0% 
Blistered 



56.53% 
36.50 
6.97 



100.0 

35.6% 
63.1 

61.3 

24.4 

41.7% 
73.9 



1.3% 

10.8% 

6.2% 



36721 

Trinidad land 

refined. 



1.4193 
Brown black 

Dull 
Homogeneous 
Semi- . 
conchoidal 

2 

Asphaltic 

188° F. 

198° F. 

0° 



1.0% 
Blistered 

3.0% 
Blistered 

54.1% 
38.0 
7.9 

100.0 



33.5% 
61.9 

64.8 

21.8 

38.2% 
70.6 



0.0% 

12.9% 

5.0% 



1 These bitumens are not strictly asphalts, as appears in the text, but may 



THE SOLID BITUMENS. 



149 



COMPOSITION OF THE MORE IMPORTANT 


ASPHALTS 




44412 

Bermudez 

refined, 1900 


67753 

Bermudez 

refined, 1903 


22220 

Cuban, 

Bejucal. 1 


13541 
Califorina, 
La Patera. 


13601 
California, 
Standard. 1 


66923 
Mara- 
caibo. 


1.0823 
Black 
Bright 
Uniform 
Semi- 
conchoidal 

Soft 

Asphaltic 

170° F. 

180° F. 

22° 


1.0575 
Black 
Bright 
Uniform 
Semi- 
conchoidal 

Soft m 
Asphaltic 
160° F. 
170° F. 
26° 


1.305 

Red-brown 

Dull 

Compact 

Semi- 
conchoidal 

2 

Asphaltic 

230° F. 

240° F. 

0° 


1.3808 

Black 

Dull 

Uniform 

Irregular 

2 

Asphaltic 
260° F. 
300° F. 
0° 


1.0627 

Black 

Dull 

Uniform 

Semi- 
conchoidal 

Soft 

Asphaltic 

170° F. 

180° F. 

0°-27° 


1.0638 
Black 
Bright 
Uniform 
Semi- 
conchoidal 

Soft 

Asphaltic 

200° F. 

210° F. 

20° 


3.0% 
Smooth 


4.4% 
Smooth 


• 88% 
Cracked 


1.5% 
Shrunken 


6.6% | 
Smooth ; 


2.7% 
Blistered 


8.2% 
Wrinkled 


9.5% 
Shrunken 


1.5% 
Wrinkled 


2.5% 
Shrunken 


1.9.9% 
Blistered 


4.7% 
Much blistc 


95.0% 
2.5 
2.5 


96.0% 
2.0 
2.0 


75.1% 
21.4 
3.5 


49.3% 
48.6 
2.1 


89.8% 
6.8 
3.4 


96.8% 
1.8 
1.4 


100.0 


100.0 


100.0 


100.0 


100.0 


100.0 


62.2% 
65.4 


69.1% 
71.9 


32.4% 
43.1 


21.6% 
43.8 


53.4% 
59.4 


45.7% 
47.2 


62.4 


67.3 


60.5 


81.4 


51.9 


46.4 


24.4 


23.4 


17:0 


8.1 


28.6 


25.3 


69.2% 
72.8 


75.9% 
79.0 


39.6% 
52.7 


• 26.7% 
54.1 


60.0% 
66.8 


51.5% 
53.2 


0.1% 


1.1% 


1.6% 


1.7% 


0.3% 


17.5% 


13.4% 


14.0% 


25.0% 


14.9% 


8.0% 


18.0% 


4.0% 




8.3% 


6.2% 







be considered as such in their relation to the asphalt paving industry. 



150 THE MODERN ASPHALT PAVEMENT. 

Warren's Characterization of Asphaltum. 1 

"A. Oils vaporizable at or about 100° or below; sparingly 
present if at all. 

"B. Heavy oils, probably of the Pittoliumor Petrolene groups; 
vaporizable between 100° and 250°, constituting some- 
times 85 per cent of the mass. 

tl C. Resins soluble in alcohol. 

&i D. Solid asphalt-like substance or substances, soluble in ether 
and not in alcohol; black, pitch-like, lustrous in fracture; 
15 to 85 per cent. 

"E. Black or brownish substance or substances, not soluble in 
either alcohol or ether; similar to D in color and appear- 
ance (Kersten); brown and ulmin-like (Volckel); 1 to 
75 per cent. 

"F. Nitrogenous substances; often as much as corresponds to 
1 or 2 per cent of nitrogen." 

He also defines asphalt as " a mixture of different hydrocar- 
bons parts of which are oxygenated." 

In the light of our present information neither the classifica- 
tion of the proximate constituents nor the definition of asphalt 
is satisfactory. 

A. Hard asphalts and but few malthas seldom contain any 
oils vaporizable at 100°. Such hydrocarbons cannot be present 
in any amount in a hard asphalt, as the material would then have 
the properties of a maltha. 

B. Heavy oils are undoubtedly the chief constituents of 
asphalt and as such require the most careful study and differ- 
entiation to determine their nature. Recent investigations have 
shown that these oils are a mixture of saturated and unsaturated 
hydrocarbons of di- and polycyclic series and of their sulphur 
and nitrogen derivatives, the sulphur derivatives being particu- 
larly characteristic of asphalt. This class of oils is that which 
we name to-day malthenes. 

C. Resins are not present in asphalt. The oils are slightly 
soluble in alcohol, but the soluble portion is not similar to resin 
in its behavior towards reagents. 

1 Descriptive Mineralogy, Dana, 6th Edition, 1896, 1017. 



THE SOLID BITUMENS. 151 

D. The substances soluble in ether are soft and resemble mal- 
thas. They are the same substances mentioned under B. They 
usually amount to from 60 to 75 per cent of the asphalt. 

E. The bitumen not soluble in ether (petroleum naphtha is 
now commonly used instead of ether as a solvent) is a hard sub- 
stance which does not melt without decomposition but is soluble 
in the malthenes, the predominating constituent of asphalt, or 
in heavy asphaltic oils. Together with the malthenes it con- 
stitutes the pure bitumen of asphalts. It contains the larger 
part of the sulphur compounds present and seems to owe its hard- 
ness to this fact. It is known as asphaltenes. 

F. Nitrogenous substances are found both in the malthenes 
and in the hard bitumens of class E. In the malthenes the nitro- 
gen derivatives have been identified as hydrocyclic bases. 

As has already been said, there is a decided difference in the 
use of the term asphalt in an industrial and specific sense. 

From investigations carried on in the author's laboratory 
within the last seven years, the results of which have been largely 
published elsewhere, 1 it is possible to characterize true asphalt more 
closely and to differentiate it specifically from other solid bitumens. 

Asphalt may be denned, industrially, as a mineral pitch, 
found in nature in a more or less solid state, melting at a tempera- 
ture in the neighborhood of that of boiling water, and miscible in all 
proportions with heavy petroleum oils or fluxes to form z viscous 
cementing material which is in use in the paving and in other 
industries. 

More specifically asphalt is a bitumen found in nature, orig- 
inating in certain types of petroleum, of various degrees of 
consistency, but generally solid, softening at a temper: ^ure in 
the neighborhood of 100 degrees Centigrade, and consisting of a 
mixture of various saturated and unsaturated hydrocarbons and 
their derivatives, a part of which are soluble in naphtha, very 
viscous liquids, largely saturated hydrocarbons unattacked by 
strong sulphuric acid in such a solvent; while those insoluble in 
naphtha are soluble in carbon disulphide and carbon tetrachloride, 



On the Nature and Origin of Asphalt, Long Island City, N. Y., 1898.. 



152 THE MODERN ASPHALT PAVEMENT. 

brittle solids which do not melt by themselves without decom- 
position on the application of heat. 

The naphtha soluble bitumen is known, conventionally, as a 
class, as ' 'Malthenes/' while the bitumen insoluble in naphtha, but 
soluble in carbon disulphide, has been called "Asphaltenes." The 
malthenes consist in part, depending upon the hardness of the bitu- 
men, of from 20 to 50 per cent of saturated di- or poly cyclic poly- 
met hylenes of the series of C n H 2n _ 2 , C n H 2n _ 4 , C n H 2n _ 8 , etc., the 
lowest member found in Trinidad asphalt being C 13 H 24 boiling at 
165° C. under a pressure of 30 mm.; in part of unsaturated hydro- 
carbons, which can be separated from the polymethylenes by 
strong sulphuric acid with which they combine readily, the nature 
of which is not so well understood; of sulphur compounds separated 
in the same way which, on isolation, are found to be the same as 
those occurring in Ohio, Canadian, and California petroleum and 
nitrogen derivatives, perhaps bearing the same relation to the poly- 
methylenes that chinolin does to benzol. The structure of these sat- 
urated hydrocarbons is given on page 105. The asphaltenes 
are probably unsaturated hydrocarbons or their derivatives, as 
they are all strongly acted upon by concentrated sulphuric acid. 
The molecules of which they consist must be highly condensed and 
have a very high molecular weight. Of their structure we know 
nothing. The asphaltenes contain the greater part of the sul- 
phur present in asphalts, and they are, as a rule, characterized 
by the presence of very considerable amounts of it, the larger 
the amount tne harder the asphalt. 1 Normal asphalts yield about 
from 10 to 15 per cent of fixed carbon on ignition, a fact which 
enables us to differentiate them by this characteristic alone from 
man} r of the other solid bitumens. 

Differentiation of the Asphalts among Themselves. — Considered 
as pure bitumens, the asphalts vary quite largely in character among 
themselves, depending upon the nature of the bitumen from which 
they have been derived, the extent to which they have been met- 
amorphosed by their environment, and the resulting difference 
in the relative proportions of malthenes and asphaltenes, and 



1 On the Nature and Origin of Asphalt, Long Island City, N. Y., 1898. 



THE SOLID BITUMENS. 153 

of saturated and unsaturated hydrocarbons which are present. 
Those asphalts which have undergone the most complete meta- 
morphism contain the largest portion of the asphaltenes and are 
the harder. A high percentage of sulphur also works in the same 
direction. Some actual variations in the amount of the total 
bitumen soluble in cold 88° naphtha in asphalts of different degrees 
cf hardness are as follows: 

No. 22220. Haxd asphalt, Bejucal, Cuba 43.1% 

•' 13541. " " La Patera, Cal. .... 43.8 

Medium hard, Trinidad 65.0 

Softer asphalt, Bermudez 69.0 

The following differences have been noted in the amount of 
sulphur found in the pure bitumen from the same localities; 

No. 13541. La Patera, Cal 6.20% 

" 22220. Cuban, "feejucal 8.28 

" 632G0. Trinidad Lake 6.16 

" 44412. Venezuela, Bermudez. 3 .93 

The asphalts can also be differentiated by their physical prop- 
erties, such as consistency, which is particularly valuable, by 
their melting-point, color, and specific gravity, though in the form 
of pure bitumen they are not very variable in the latter respect, 
and by other minor differences. 

Asphalt Associated with Mineral Matter. — In the preceding 
paragraphs, asphalt has been considered as a more or less pure 
bitumen, but it is more often than not associated with mineral 
matter of one kind or another. This fact has resulted in a classi- 
fication of this material on this ground alone, according to the 
nature of the mineral matter. Such a classification may be of 
some industrial value, although having nothing to do with the 
character of the asphalt itself. At best it is artificial. The fol- 
lowing, based on the writer's investigation of a large number of 
asphalts from all over the world, is suggested: 

Asphalt. — 1. Impregnating compact, amorphous limestones 
to the extent of less than 16 per cent. 

2. Impregnating limestones, partially crystalline and mixed 
with silica or silicates, to the same extent. 



154 THE MODERN ASPHALT PAVEMENT. 

3. Impregnating fossiliferous limestones to the same extent. 

4. Impregnating shales or schists. * 

5. Impregnating hard sandstones. 

6. Mixed with silica and clay to a fixed and uniform extent 
at the source where the asphalt originates. 

7. Mixed with sands by percolation into beds of the latter in 
place. 

8. Mixed with soil and organic matter of vegetable origin 
where the effusion of tar springs have hardened on exposure. 

Type 1 is found on the continent of Europe, in Sicily, Val de 
Travers, Seyssel, and in the United States but to a limited extent 
in Utah. 

Type 2 is found in Oklahoma, near Ravia and elsewhere. 

Type 3 occurs near Dougherty in Oklahoma, the rock being 
a member of the lower coal measures, according to Eldridge, and 
in the neighboring Buckhorn District. • 

Type 4 is found in Ventura County, California. 

Type 5 is found in the same locality. 

Type 6 is unique, Trinidad Lake Asphalt. 

Type 7 includes large deposits of sand in Kentucky and Cali- 
fornia, which are saturated, in situ, with a rather soft asphalt. 

Type 8 is found wherever exudations of bitumen have spread 
over the soil and become hardened by exposure. They are com- 
mon in Kern County, California. 

It appears, therefore, that the character of the mineral matter, 
with which an asphalt is mixed naturally, must be considered 
as well as the nature of the bitumen itself, in forming an opinion 
of its availability for paving purposes. 

With the information which has been presented in the preced- 
ing pages it is now possible to consider individually each of the 
native bitumens, known generically or specifically as asphalts, 
and afterwards to make a comparative study of their availability 
in the paving industry. 



THE SOLID BITUMENS. 155 



SUMMARY. 



Asphalt is a term which may be used either industrially 01 
specifically; industrially to cover all the solid native bitumens 
used in the paving industry and specifically to include only such 
as melt on the application of heat, at about the temperature of 
boiling water, are equally soluble in carbon disulphide and car- 
bon tetrachloride and to a large extent in 88° naphtha, those 
hydrocarbons soluble in naphtha consisting to a very consider- 
able degree of saturated hydrocarbons, yielding about 15 per cent 
of fixed carbon and containing a high percentage of sulphur. 
Under this definition it can be seen that grahamite is not an asphalt, 
since it is not largely soluble in naphtha and yields a very high 
percentage of fixed carbon on ignition. It is also less soluble in 
carbon tetrachloride than in carbon disulphide. Gilsonite is not 
an asphalt, since the saturated hydrocarbons contained in the 
naphtha solution are very small in amount and quite different 
in character from those found in asphalt. 



CHAPTER X. 
INDIVIDUAL ASPHALTS. 

Trinidad Lake Asphalt. — In considering the asphalts indi- 
vidually, it will be best to examine in detail the characteristics 
of the one in regard to which the most is known and with which 
the most successful pavements have been laid and then to com- 
pare others with it. Trinidad lake asphalt is, of course, the 
one referred to. The location of the deposit and the manner of 
its occurrence may be summarized as follows: 1 

" The island of Trinidad lies off the north coast of South 
America, between 10° and 11° of latitude and 61° and 62° of longi- 
tude (Fig. 4), It is bounded on the north by the Caribbean Sea, 
on the east by the Atlantic, on the south by a narrow channel, 
into which flow the waters of the northern and most westerly 
mouths of the Orinoco, and on the west by the Gulf of Paria, 
the two latter bodies of water separating it from the mainland 
of Venezuela. . . . 

" While there are deposits of pitch scattered all over the island, 
the only ones of commercial importance are those situated on 
La Brea Point, in the wards of La Brea and Guapo, in the county 
of St. Patrick, on the western shore of the island. They are 
about 28 miles in an air line from Port of Spain, the seat of govern- 
ment, the chief harbor and only port of entrance, and lie on the 
north shore of the southwestern peninsula, the point upon which 
they are situated being apparently preserved from destruction 
by the sea, which is elsewhere rapidly wearing away the coast 
by the bituminous deposits which exist along the shore and even 

1 Report of the Inspector of Asphalt and Cements, Eng. Dept., District 
of Columbia, 1892. On the Nature and Origin of Asphalt, Long Island City, 
N Y., 1898. 

156 



INDIVIDUAL ASPHALTS. 



157 



some distance from it, and which from their toughness resist the 
action of the waves better than the soft rocks of this region. The 
pitch deposits are found scattered over the point, but can be divided 
conveniently into two classes, according to their source. 

" The main deposit is a body of pitch known as the Pitch 
Lake, situated at the highest part of the point. 

" Between this and the sea, and more especially toward La 
Brea, are other deposits, covered more or less and mixed with soil. 




Fig. 4. 

" The pitch from these sources is classed as ' lake pitch ' and 
1 land pitch.' 

" By far the largest amount of pitch is found in the pitch lake, 
originally nearly a circular area of 127 acres, the surface of which, 
in 1894, was 138.5 feet above sea level. From the lake the ground 
falls away on all sides, except, perhaps, a slight ridge to the east 
and southeast. In fact it seems plain that this deposit lies in 
the crater of a large mud volcano which has filled up with pitch." 

It appeared, when first examined by the author in 1891, "as 
a flat, gently sloping mound, wooded over a large portion, open 
savanna elsewhere, and toward the northeast merely grassed over. 



158 THE MODERN ASPHALT PAVEMENT. 

" On the west its slopes toward the sea are gentle for some 
distance, but then more abrupt. On the north, toward La Brea 
Point, the reverse is the case, and a ravine runs, with a small 
stream, quite to the village, this slope being very scantily covered 
by a growth of coarse grass near the lake, becoming more bushy 
farther on, while the other slopes are well wooded, with magni- 
ficient palms near the lake, forming a beautiful band or border 
around it, within which is a grassy zone of about 100 to 200 feet 
or more in width." 

Since then the removal of large quantities of pitch has quite 
changed the surroundings, owing to the cutting off of the wood 
and other alterations resulting from the operations incident to 
the exportation of asphalt. 

In 1893 a series of borings were made upon the lake by the 
New Trinidad Lake Asphalt Company. 

" A boring at the center of the lake was carried to a depth 
of 135 feet, the entire distance being through pitch, which, as 
far as ocular evidence goes, has the same character as that at 
the surface. It was impossible to carry the boring deeper, as 
the movement of the pitch had so inclined the tube — one foot 
in six — which formed the lining, that it had to be abandoned. 
It then gradually toppled over and was engulfed. Nothing has 
been seen of it since. The result was sufficient, however, to show 
the great depth cf the crater and the uniformity of the pitch. 
The depth attained was within a few feet — not more than three 
and a half — of sea level, and yet we do not know how much deeper 
the pitch may extend. The borings on the north side of the lake 
about 1000 feet from the centre, and 100 feet from the edge, was 
in pitch of the usual character for 75 feet, showing a very steep 
slope to the sides of the crater. At -80 feet a layer of fine white 
sand was met for a few feet, and then asphalt was again encount- 
ered. At 90 feet sand mixed with asphalt was struck, and this 
continued to a depth of 150 feet. 

" Further borings, made at some distance from the lake, gave 
results near the surface which were similar to those found at the 
deeper levels at the edge of the lake. Sand, mixed with asphalt 
here and there, was the common material, while at a depth of 



INDIVIDUAL ASPHALTS. 159 

80 feet on the southern side of the lake, and about 80 feet south 
of the road, and between 1200 and 1300 feet from the centre of 
the lake, a very hard asphaltic sandstone was found. 

" All the evidence thus goes to show that the sides of the crater 
are of sand or sandstone, more or less impregnated with bitumen, 
the sandstone being no doubt the rock of the hillside toward the 
south, against which the crater has been built up. 

" From the borings it was thus learned for the first time how 
enormous the deposit was, and the idea that the mound was really 
a crater seemed to be confirmed. It is, nevertheless, hard to 
realize that there is at this point, 138 feet above the sea, a bowl- 
like depression over 2300 feet across, and over 135 feet deep, 
reaching below the sea level, and filled with a uniform mass of 
pitch, which must amount to over 9,000,000 tons." 

Crude Trinidad asphalt is an extremely uniform mixture 
or emulsion of gas, water, fine sand, clay and bitumen which are 
found in the following proportions: 

Bitumen 39.3% 

Mineral matter 27 . 2 

Water of hydration of clay 3.3 

Water and gas, loss at 325° F 29 .0 



98.8% 



The material is of the greatest uniformity in composition, as 
it has been found that specimens collected at intervals of 100 feet 
and at a depth of 1 foot over the surface of the deposit and to a 
depth of 135 feet at the centre all have the same composition as 
appears from the following table. 

The amount of uncombined water does not appear among the 
constituents in these determinations as, in order to avoid any 
possibility of change, it was removed by air-drying at the lake 
in the course of the 'preparation of the samples for transportation 
to the United States. Frequent examinations of the crude asphalt 
in a fresh condition have shown, however, the water to be as con- 
stant in amount as the other constituents. 

In this deposit there are, therefore, many millions of tons of 
asphalt of a highly uniform composition, not only as far as the 



160 



THE MODERN ASPHALT PAVEMENT. 



AVERAGE COMPOSITION OF TRINIDAD LAKE ASPHALT IN 

CIRCLES. 



Circle 2: 

4: 



2C0 feet from centre 
4C0 



6: 600 

8: 8C0 

10: 1000 

12: 1100 

General Average 

Circle 14 : 1400 feet from centre 



Bitumen 

by CS 2 . 



55.02% 

54.99 

54.84 

54.66 

54.78 

54.62 

54.92 

53.86 



Mineral 

Matter 

on 

Ignition. 



35.41% 

35.40 

35.49 

35.56 

35.44 

35.45 

35.46 

36.38 



Differ- 
ence 
Undeter- 
mined.* 



57% 
61 

67 
78 
78 



9.93 
9.72 
9.76 



Soluble 

in 
Naptha. ; 



31.83% 

31.63 

31.85 

31.67 

31.58 

31.77 

31.72 

30.52 



Total 
Bitumen 

thus 
Soluble. 



57.85% 

57.55 

58.26 

57.97 

57.64 

57.51 

57.79 

56.66 



AVERAGE COMPOSITION OF TRINIDAD LAKE PITCH FROM 
THE BORING. 



From surface to 135 feet in depth. 



54.66% 



35.90% 



9.44% 



31.53% 



57.67% 



* This naphtha possessed less solvent power than usual. 

2 Water of clay, not lost on refining, bitumen held by clay and inorganic salts, volatil- 
ized on ignition. 

proportions of bitumen and mineral matter are concerned, but 
also in the relation of the malthenes to the asphaltenes. 

Constitution of Crude Trinidad Asphalt. — The constitution of 
the material forming the great deposit found in the Pitch Lake 
in the Island of Trinidad has only been explained very recently. 
In the course of the ordinary routine analysis of the substance 
from which the water has been removed, it is found that the 
summation of the percentages of bitumen soluble in cold carbon 
disulphide and of the mineral matter obtained by ignition does 
not amount to 100, as is seen in the above table. It has been the 
custom for many years to call the difference between this sum 
and 100 "organic matter not bitumen." Recent investigations 
of the author l have shown that this is an entirely incorrect state- 
ment, as the asphalt contains practically no organic matter not 



1 The Proximate Composition and Physical Structure of Trinidad Asphalt, 
Proc. Am. Soc. Test. Materials, 1906, 6, 509. 



INDIVIDUAL ASPHALT. 161 

bitumen, and that the undetermined matter or difference can 
be readily explained as follows: 

Water and Gas. — If a weighed amount of crude Trinidad 
asphalt, immediately after being taken from the deposit, is ground 
to a fine powder and exposed to the air for twenty-four hours, it 
will lose about 29 per cent of water and a small additional amount 
on further exposure in vacuo over sulphuric acid, this latter 
small amount being very probably water of crystallization of the 
salts which are present. The total loss averages 29 per cent, 
with but very small variation, in the fresh pitch taken several 
inches below the surface, although on exposure to the air for 
some time a very considerable proportion of this amount may be 
lost, as in the case of storage of the crude material. 

At the same time with the water the gas which it contains 
in solution, consisting of a mixture of carbon dioxide and hydrogen 
sulphide, is lost. Its percentage must be extremely small by weight. 

Having determined the average amount of water in the fresh 
pitch with some degree of accuracy it will be convenient to con- 
duct the further investigation of the pitch on the dried or refined 
material. 

Mineral Matter. — The residue of mineral matter obtained 
on the ignition of refined Trinidad asphalt in a muffle averages, 
as the result of fifteen determinations of representative samples, 
36.5 per cent corresponding to 25.9 per cent in the original crude 
material, with extremes of 36 and 36.8 per cent. As this igni- 
tion has taken place at a temperature approaching 800 degrees 
Centigrade, there is every reason to believe that considerable 
inorganic matter has been volatilized, as is often found to be the 
case in the preparation of the ash of vegetable material. In the 
latter case the addition of tricalcium phosphate prevents such loss 
and it seemed that this mode of procedure might be applicable 
to the asphalt. When the latter was ignited in the presence of 
the phosphate a residue greater by 2 per cent was obtained, 38.5 
per cent, and one which more correctly represents the percent- 
age of anhydrous inorganic matter present in the asphalt, showing 
that 2 per cent is volatilized in the ordinary course of ignition, 
thus accounting for that amount of the ' 'undetermined matter." 



162 



THE MODERN ASPHALT PAVEMENT. 



The mineral matter on examination is found by elutriation to 
consist to a large extent, 30 to 40 per cent, of clay and, of course, 
its water of hydration, which may be properly regarded as a part 
of the mineral matter originally present, is lost on ignition. If 
the residue after the extraction of the asphalt with solvents is 
heated to a temperature of 340 degrees Centigrade, it loses from 

4 to 6 per cent, the determination at such a temperature 
of course not being one capable of being made with great accuracy. 
A certain, amount of this loss is plainly due to the volatilization 
or destruction of bitumen held by the clay present, as shown by 
its condensation on the side of a glass tube in which the heating 
is conducted, but as this amount, as will appear later, cannot 
exceed 1 per cent, the loss due to the presence of water in the clay 
must reach at least 4.5 per cent. The total loss on ignition of 
bitumen and water in the clay must, however, amount to about 

5 per cent and be included in the "undetermined matter." When 
this per cent is added to the 2 per cent of inorganic matter vol- 
atilized at 800 degrees Centigrade, the entire percentage of 
undetermined matter obtained by the usual method of analysis 
is accounted for, so that it appears that Trinidad asphalt really 
contains practically no organic matter not bitumen. 

In order to determine whether this assumption is correct, 
analyses have been made of mixtures of an extremely pure bitumen, 
gilsonite, with clay and other fine inorganic materials, the mixture 
being prepared by melting the "bitumen, stirring being kept 
up during cooling, and the cold brittle mixture being then ground 
to a fine powder in order to obtain a uniform mixture for 
analysis. The results of an examination of such mixtures by 
the routine methods are as follows: 



Bitumen sol- 
uble in Car- 
bon Disul- 
phide. 



Mineral 

Residue on 

Ignition. 



Undeter- 
mined. 



Fullers earth, air dried 

" " ignited 

Brick clay, air dried 

" ignited 

Portland cement, ignited ....... 

Trinidad mineral residue, ignited 



62.3% 

59.7 

72.3 

77.9 

82.6 

64.4 



28.8% 

34.1 

22.9 

17.9 

15.8 

34.3 



8.9% 

6.2 

4.8 

4.2 

1.6 

1.3 



INDIVIDUAL ASPHALTS. 



163 



It appears from the preceding results that all the artifical 
mixtures of bitumen and fine mineral matter apparently contain, 
as the result of the analyses, a certain amount of undetermined 
matter or organic matter not bitumen, although from the nature 
of these mixtures nothing of this kind can be present. The amount 
varies from 8.9 per cent in the case of the unignited Fullers earth, 
to 1.3 per cent for the ignited mineral residue of Trinidad asphalt. 
The larger percentage is due to the presence of water of hydration 
in the Fullers earth, while the smaller percentage shows that the 
mineral matter in Trinidad refined asphalt is capable of retaining 
1.3 per cent of bitumen, either by absorption, adsorption, or both. 
Our assumptions in regard to the true composition of Trinidad 
asphalt are, therefore, correct and its actual composition should 
be stated as follows: 





Crude Trinidad 
Asphalt. 


Refined 

Trinidad 

Asphalt. 


Water and gas 


29.0% 
39.0 
.3 

27.2 
3.3 




Bitumen soluble in cold carbon disulphide 

Bitumen retained by mineral matter 


56.5% 
.3 


Mineral matter, on ignition with tricalcium 
phosphate 


38.5 


Water of hydration, clay, and silicates 


4.2 








98.8% 


99.5% 



Refined Trinidad Lake Asphalt. — Refined Trinidad lake asphalt, 
which is dried with steam and agitated with steam, has the charac- 
teristics given in the table on pages 164 and 165. 

Refined Trinidad Lake asphalt is of a homogeneous structure 
and uniform composition except in so far as the percentage of 
mineral matter and consequently of bitumen may vary, being 
greater in one sample than another, through sedimentation caused 
by the lack of agitation during cooling. It possesses none of the 
emulsion structure seen in the crude material. It has a dull 
conchoidal fracture, no lustre, a blue-black color in powder and 



164 THE MODERN ASPHALT PAVEMENT. 

REFINED TRINIDAD LAKE ASPHALT. (AVERAGE COMPO- 
SITION.) 

Test number 63260 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F , original substance, dry. ... 1 .40 

Color of powder Blue-black 

Lustre Dull 

Structure Homogeneous 

Fracture Semi-con choidal 

Hardness, original substance. 2 

Odor Asphaltic 

Softens 180° F. 

Flows 190° F. 

Penetration at 78° F 7° 

CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 1.1% 

Character of residue Smooth 

Loss, 400° F., 7 hours (fresh sample) 4.0% 

Character of residue Blistered 

Bitumen soluble in CS 2 , air temperature 56 .53% 

Difference undetermined 8 . 97 

Inorganic or mineral matter 36 . 50 

100.00 
Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 35 . 6% 

This is per cent of total bitumen C3 . 1 

Per cent of soluble bitumen removed by H 2 S0 4 61. 3 

Per cent of total bitumen as saturated hydrocarbons 24 . 4 

Bitumen soluble in 62° naphtha 41 . 7% 

This is per cent of total bitumen 73 . 9 

Carbenes: 

Bitumen more soluble in carbon tetrachloride, air tem- 
perature, than in bisulphide of carbon 1 . 3% 

Bitumen yields on ignition: 

Fixed carbon ] 0.8 

Sulphur. 6.2 



INDIVIDUAL ASPHALTS. 



165 



REFINED TRINIDAD LAKE ASPHALT. 
COMPOSITION.) 



(EXTREMES IN 



PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 

Softens 

Flows 

Flow in per cent of average 

CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours 



Loss, 400° F., 7 hours (fresh sample). 
Bitumen soluble in CS-. 



Malthenes : 

Per cent of total bitumen soluble in 88° naphtha, 
air temperature 



Per cent of total bitumen soluble in 62° naphtha . 

Bitumen yields on ignition: 

Fixed carbon 



1.405 

180° F. 

190° F. 

90% 



1.5% 

3.5% 
57.0% 

68.0 s 
77.0 

10.0 



1 Percentage depends upon the character of solvent naptha and method of treatment. 

an asphaltic odor. It softens and flows below the temperature of 
boiling water, but becomes liquid only at much higher tempera- 
tures, about 300° F. Its density is high as compared with most 
other bitumens, 1.40, owing to the mineral matter which it contains. 

Refined Trinidad asphalt differs slightly in composition from 
the crude material, or rather from this material after the removal, 
without the aid of heat, of the water which it contains, owing to 
the volatilization, at the higher temperature used in refining, of 
certain constituents not driven off at the temperature of boiling 
water. 

The Mineral Matter in Trinidad Asphalt.— The mineral matter 
in Trinidad lake asphalt is as much a fixed constituent of the 
material as the bitumen. It is not accidental or adventitious as 
it would then vary in amount. It has evidently become mixed 
with the bitumen under fixed and invariable conditions at some 
subterraneous point where the bitumen originates and meets an 
environment that results in the production of the asphalt itself. 

It is in an extremely fine state of subdivision. On sifting 
the particles are found to be of the size given below: 



166 THE MODERN ASPHALT PAVEMENT 

I 

Passing 200-mesh sieve 08 mm. 89.8% 

" 100- " " 17 " 8.0 

" 80- " " 20 " 2.2 

100.0 

And on elutriation of the 200-mesh material: 

Subsiding in 15 seconds, smaller than .08 mm. 24.3% 

" " 1 minute, " " .05 " 13.1 

" "30 minutes, " " .025 " 46.7 

After " " " " .0075 " 15.9 

100.0 

Under the microscope it is found to be composed principally 
of quartz with clay and the residue of the salts from the mineral 
water originally emulsified with the crude bitumen. The quartz con- 
sists of very sharp flakes, Fig. 2, No. 8 7 and their appearance leads 
one to believe that it has originally been in solution under enormous 
pressure in the thermal water, from which it has separated on 
the release of the pressure or on cooling, and has finally flown 
into fragments on further reduction of the pressure to that of 
the atmosphere. The presence of the clay is more difficult to 
explain. It is sufficient to know from the point of view of the 
engineer that the mineral matter is extremely fine, is most inti- 
mately mixed with the bitumen by nature and is consequently 
the most perfect form of filler, far exceeding anything which can 
be artificially mixed with a purer asphalt, and as such a most 
desirable constituent. 

The clay, when it has been freed by treatment with acid from 
the oxide of iron which colors it the characteristic flesh-pink color 
of the ash of Trinidad asphalt and which is derived from the iron 
salts in solution in the thermal water, is a pure white, impalpable 
powder which amounts to not more than one-third of the entire 
mineral matter. 

The mineral matter also contains constituents, other than vhe 
iron, derived from the thermal water, principally sulphates and 
chlorides of soda, but as the entire amount of salts in the thermal 
water is less than 2 per cent, these so-called soluble salts can amount 
to no more than 1 per cent of the refined asphalt and probably 



INDIVIDUAL ASPHALTS. 



167 



much less, as a part is volatilized in refining and a part rendered 
insoluble. Actual extraction of the refined asphalt when most 
thoroughly carried out yields only two-tenths of 1 per cent of 
soluble salts. 

The composition of the mineral matter is as follows: 





Soluble in Acid. 


Insoluble. 


Total. 


Silica, Si0 2 


7.38 

6.30 
0.46 
0.11 
1.56 
0.35 
0.97 
0.22 

17.35 


70.64 
9.66 
1.32 
0.24 
0.79 


70.64 


Alumina, A1 2 3 


17 04 


Ferric oxide, Fe 2 3 1 


7.62 


Lime, CaO 


70 


Magnesia, MgO 


0.90 


Soda, Na 2 


1.56 


Potassium, K 


0.35 


Sulphuric oxide, S0 3 


0.97 


Chlorine, CI 


0.22 








82.65 


100.00 


iFeOi 


lot determined. 







Some of the mineral matter is so impalpably fine that it will 
not separate from a solution of melted or dried Trinidad pitch 
in any of the usual solvents even after months of standing and 
many hours' treatment in a centrifugal. It will pass also through 
the finest filters. It has been thought by Peckham and others, on 
this account, to be chemically combined with the organic com- 
pounds of the asphalt but the author has found that by con- 
tinued swinging of a solution of the asphalt in carbon disulphide 
in a centrifugal it can be so far reduced that it amounts to but 
2 per cent, and when the bitumen thus purified is dissolved in 
chloroform or bisulphide of carbon and passed through a biscuit 
filter all the mineral matter is removed, leaving an absolutely 
pure bitumen. This is not surprising, since the smaller amount 
of mineral matter finally removed is a ferruginous clay and could 
not possibly be combined with the organic matter in a chemical 
way, although it no doubt is in a state of close physical combina- 
tion. In this connection the conclusions of Dr. Allerton S. Cush- 
man of the Office of Public Roads of the U. S. Department of 
Agriculture on the porosity of clay particles is of interest. 



168 



THE MODERN ASPHALT PAVEMENT. 



The very finest mineral matter which is separated from Trini- 
dad lake asphalt has the following composition: 



ANALYSIS OF FINEST MINERAL MATTER. 





Insoluble 
inHCl. 


Soluble. 


Total. 


Si0 2 


32.36 

6.74 

1.40 

.45 

.34 


33] 64 
11.74 
3.20 
1.40 
1.18 
.53 
7.16 


32.36 

40.38 

13.14 

3.65 

1.83 

1.18 

.53 

7.16 


ALA 

Fe 2 3 

CaO '.. 


MgO 


K 2 


Na 2 


S0 3 . 


41.29 


58.85 


100.23 



The Bitumen of Trinidad Lake Asphalt. — The bitumen of Trin- 
idad lake asphalt amounts to about 56 per cent of the refined 
material. It is a lustrous black pitch like all pure bitumens. It 
has a specific gravity of 1.06 to 1.07 and retains in suspension very 
persistently amounts of the finest mineral matter of the asphalt, it 
being only possible, as has been shown, to remove this by passing its 
solution in bisulphide of carbon through a biscuit-filter of the Pasteur 
type. In this way it can be obtained in an absolutely pure form. 
In this condition it has the composition given in table on p. 169. 

This bitumen is characterized by the large percentage of sul- 
phur which it contains, and the presence of nitrogen. There are 
apparently no oxygen derivatives present in the pure bitumen, 
or they occur in very minute amounts, that is to say, they are 
insoluble in chloroform or carbon disulphide. 

It is characterized also by its great stability or lack of liability 
to change or volatilize at high temperatures. When 20 grams 
of the materials are heated in a glass crystallizing dish to 325° F., 
according to the method described in Chapter XXVIII, it loses 
but 1 per cent, and only 4 per cent when exposed to a tempera- 
ture of 400° F. for 7 hours. 



INDIVIDUAL ASPHALTS. 169 

TOTAL BITUMEN IN TRINIDAD LAKE ASPHALT. 



Preparation. 


I. 


IV. 


V. 


Average. 


Carbon 


82.59 

10.74 

6.04 

0.51 


81.95 

10.51 

6.54 

0.92 


82.44 

10.81 

5.90 

1.00 


82.33 


Hydrogen 


10.69 


Sulphur 


6.16 


Nitrogen 


0.81 








99.88 


99.92 


100.15 


99.99 



Of the total bitumen about 63 per cent, when the process of 
extraction is carried out according to the method described in 
the chapter referred to, is in the form of hydrocarbons of the 
class known as malthenes, soluble in 88° B. naphtha, having a 
density of .994. The malthenes are soft and exceedingly sticky, 
like maltha. When they are treated with strong sulphuric acid, 
according to the author's method, all but 39 per cent prove to 
be unsaturated hydrocarbons which readily enter into combina- 
tion with acid. This means that but 24 to 25 per cent of the 
total bitumen in the asphalt consists of saturated hydrocarbons. 
On ignition these malthenes yield 6.3 per cent of fixed carbon. 
This is about the same percentage that is found for the denser 
California fluxes and for the lighter natural malthas. 

The malthenes can be fractioned in vacuo into hydrocarbons 
of different boiling-points, and from them can also be obtained 
the nitrogen and sulphur derivatives corresponding to those found 
by Mabery in the sulphur petroleums, all of which have been 
described bv the author elsewhere. 1 

It is sufficient to state here that the saturated hydrocarbon of 
lowes boiling-point and molecular weight, which has been sepa- 
rated from the malthenes of Trinidad lake asphalt, has the follow- 
ing properties: 

Boiling-point at 30 mm. 165° C. 

Specific gravity at 25° C 8576 

Refractive index 1 . 4650 

Carbon 86 .85% 

Hydrogen 13.34 

1 On the Nature and Origin of Asphalt, Long Island City, N. Y., 1898. 



170 



THE MODERN ASPHALT PAVEMENT. 



Such a hydrocarbon would correspond to one of the CnH2n-2 
series having the formula C13H24, which contains 86.67 per cent 
of carbon and 13.33 per cent of hydrogen. That this is the formula 
has been confirmed by determinations of the molecular weight 
of the substance, and its molecular refraction. Of the consti- 
tution of the hydrocarbons of asphalt something has been said 
in a preceding chapter. 

The bitumen of Trinidad asphalt which is insoluble in 88° 
naphtha is of the class known as the asphaltenes, according to our 
purely arbitrary classification; the relative proportion of the two 
forms of bitumen, asphaltenes and malthenes, being dependent upon 
the nature of the solvent used, so that any information derived from 
a determination of the percentages of the two classes of hydro- 
carbons will be purely relative as compared with other bitumens 
which have been examined by exactly the same methods and with 
the same solvents. Trinidad asphalt contains a very small amount 
of bitumen which is soluble in chloroform, carbon tetrachloride, 
and turpentine, and which is not soluble in carbon disulphide, as 
shown by Peckham. 1 

The asphaltenes are hard, brittle bitumens which do not melt 
but only intumesce on heating, and in this respect, as well as in 
the percentage of fixed carbon which they yield, 25.8 per cent., 
correspond closely with the softer grahamites. The asphaltenes 
are soluble in the heavy asphaltic oils. 

The ultimate composition of the malthenes and asphaltenes 
in Trinidad lake asphalt is as follows, as compared with that of 
the total bitumen previously given: 





Malthenes. 


Asphaltenes. 


Pure Bitumen. 


Carbon 


84.6 

11.3 

2.9 

.6 

99.4 


82.0 

7.8 

10.9 


82 33 


Hydrogen 


10.69 


Sulphur 


6 16 


Nitrogen 


81 








100.7 


99.99 



1 Am. J. Science, 1896, [4], 151, 193. 



INDIVIDUAL ASPHALTS. 171 

The saturated hydrocarbons in the malthenes have the follow- 
ing composition: 

Specific gravity 976 

Carbon 86.40 

Hydrogen 12.70 

Sulphur 45 

Nitrogen 07 

99.62 

From these figures it appears that the sulphur derivatives 
are largely contained in the asphaltenes and in but relatively 
small amounts in the malthenes, while they are almost completely 
removed from the latter by treatment with strong sulphuric acid. 
From the ultimate composition of the saturated hydrocarbons 
contained in the malthenes it is evident that these belong to a 
series in which the number of hydrogen atoms is considerably 
below twice the carbon atoms, that is to say, they must be di- 
or poly cyclic polymethylenes, and very similar to those which 
are found in Texas, California, and other asphaltic oils. 

With the aid of the above data some insight may be gained 
of the character of the bitumen of Trinidad lake asphalt. In 
other asphalts and solid bitumens the proportion of malthenes 
to asphaltenes may be greater or less, while the amount of satur- 
ated hydrocarbons which they contain may vary. If we accept 
the bitumen of Trinidad lake asphalt as our standard and refer 
others to it, by making the same determinations of their character- 
istics as has been done with the type bitumen, it is possible to 
differentiate them more or less satisfactorily. 

Trinidad Land Asphalt. — Of the Trinidad land asphalt deposits 
the author wrote, in 1892, as follows: 

" La Brea Point consists of a mass of hardened pitch deposits 
and reefs extending some distance into the gulf and along the 
shore in both directions. The deposits are found in greater or 
less abundance at all points between the shore and the lake, and 
directly along the line of the road, over an area estimated at a 
thousand acres or more. Two feet or more of soil cover the deposit 
at some distance from the lake, but near it the thickness diminishes 
and at places bare pitch is found. 



172 THE MODERN ASPHALT PAVEMENT. 

" On the point the pitch of the reefs is hard and resonant and 
has no cementitious value. The nearer the deposits are to the 
lake, however, the softer they become. 

" The incline from the lake to the gulf, a distance of three j 
quarters of a mile, is at first about oaie in twenty-five, gradually 
diminishing to the shore. Near the edge of the lake there is now 
a rank growth of grass, followed by. shrubs and trees after passing 
the forks of the road. In the village, cultivated land is found, 
and large pits filled with stagnant water, from which pitch has 
been excavated. Except very near the lake, the pitch excavated 
from the land deposits is of a very different appearance from that 
taken from the lake, and it is also of several kinds. 

" The conchoidal masses removed from the lake, as I have 
said, contain large gas cavities, and in appearance and somewhat 
in consistency resemble a black Swiss cheese. On this account 
the land pitch most nearly resembling this is known as ' cheese 
pitch.' It occurs in different degrees of porosity and life. In 
addition, land pitch is found in solid masses scarcely to be dis- 
tinguished from refined asphalt, and this is known as ' iron pitch/ 
Pitch, known as ' cokey pitch/ from having been coked by the 
burning of the brush over its surface, and the chocolate and friable 
alteration products which have originated from atmospheric 
action and disintegration, are also recognized." 

Again in another place in the same report: 

" In past times the pitch very probably continued to collect 
(in the lake) until it overflowed the rim of the crater, in many 
directions, and thus perhaps became the source of many of the 
land pitch deposits now found from the end of the lake to the sea." 

It has also been claimed that the land pitch has reached its 
present position by being forced up through the soil from the 
same source from which the lake derives its material. 

For the purpose of looking into the nature of the material 
from the point of view of its suitability for the asphalt paving 
industry this is immaterial. It is the nature and characteristics 
of the land asphalt deposits as they are available commercially 
which are of interest at this point. 

Trinidad land asphalt differs from that found in the lake deposit 



INDIVIDUAL ASPHALTS. 173 

as the result of such changes as have been brought about by its 
having been buried under soil and exposed to the action of ground- 
water and aging for many centuries, that is to say, it is a very 
much weathered material. The two materials are undoubtedly 
derived from the same original subterranean source. The land 
asphalt may, as has been said, have reached its present position 
either by overflow from the lake or by intrusion into its present 
position in the soil directly from the point of origin. In either 
case no land asphalt has been found which has not been altered 
in its nature owing to its present or past environment, so that 
it differs essentially from the lake material. 

Land asphalt is very variable in character, depending upon the 
length of time during which it has been subjected to weathering. It 
is much less cheesy than lake asphalt, that is to say, it contains 
a smaller number of gas cavities, and is harder. Some of it has 
been converted by brush fires into a hard compact pitch without 
gas cavities, resembling refined asphalt which, from its hardness, 
is known as iron pitch. Some portion of the land asphalt has 
been converted even to coke. These two latter forms are of no 
interest to the paving industry and are carefully removed from 
the material which is collected for this purpose. Further weather- 
ing of the material from the action of soil-water converts it into 
a substance of a chocolate color, which is very friable. Where 
the weathering is carried to its ultimate conclusion only the fer- 
ruginous mineral matter is left, of a bright-red color, as is evident 
on the beach; where the asphalt is subjected to the continuous 
action of sea water it becomes very hard but is not weathered 
to any further degree. That is to say, water containing the salts 
found in sea water does not act upon it. This is important in 
connection with the claims that soluble salts cause disintegration 
of Trinidad asphalt. 

Much of the asphalt found in the land deposits plainly orig- 
inated in the so-called lake and is now found mingled with the 
soil after it has run over the rim of the lake. In consequence, 
the land asphalt nearest the lake is much less weathered than 
that at a distance. The difference can be seen from toe following 
analyses of specimens collected near the lake and at intervals 



174 



THE MODERN ASPHALT PAVEMENT. 



between it and the shore.. For comparison an analysis of lake 
asphalt is given: 

AVERAGE COMPOSITION OF LAKE PITCH, DRIED IN VACUO, 
KEARNEY COLLECTION. 



Average. 



Bitumen 

Soluble CS 2 . 



54.25% 



Mineral 
Matter. 



36.51% 



Difference 
Undeter- 
mined. 



9.24% 



Bitumen 

Soluble 

Petroleum 

Naphtha. 



Total 
Bitumen 
Soluble in 
Naphtha. 



35.41% 



65.27%, 



AVERAGE COMPOSITION OF LAND PITCH, DRIED IN VACUO, 
KEARNEY COLLECTION. 



Ei^ht specimens froia Lot C, near the lake. 



Average. 



54.03% 



36, 



9.48% 



33.02% 



Four specimens from Crown Land Lots adjoining C. 



Average. 



53.81% 



36 . 62% 



.57% 



32.29% 



Five specimens from east of road, middle ground. 



Average. 



52.31% 



37.80% o 



9.89% 



31.25% 



Seven specimens from Village Lots, near the Gulf. 



Average 

General average. 



52.27% 
53.10 



37.73% 
37.16 



10.01% 
9.74 



31 42% 
31.99 



61.11% 



60.01% 



59.74%, 



60.12% 
60.14 



It is apparent that the effect of weathering has been com- 
paratively small in the deposits closely adjoining the lake, but 
that, as we proceed further on toward the shore, the change is 
more marked and is particularly evidenced by the decrease in 
bitumen present, and decrease in the percentage of malthenes. 
The lake pitch, so-called, has, with the naphtha used as a solvent, 
65.3 per cent of its bitumen soluble in naphtha, while just outside 
the lake the land pitch has only 61.1 per cent, and further on only 
59.7 per cent soluble. This may seem a small difference, but it 



INDIVIDUAL ASPHALTS. 175 

is evidence of a large change. In glance pitch, examined in the 
same way, 24 per cent only of the entire bitumen was found to 
be soluble in naphtha, in lake pitch 65.3 per cent. Land pitch 
may, therefore, be inferred to be partly converted from lake to 
glance pitch. 

The composition of an average commercial refined land 
asphalt as compared with the average lake material is well shown 
in the table on page 176. 

Land asphalt being so dependent upon its environment for 
its character, it is hardly possible to determine its average com- 
position. The extremes which are met with in recent commer- 
cial supplies are of interest (see table, page 177). 

From these figures it appears that refined Trinidad land 
asphalt of good quality is differentiated from the lake supply by its 
higher specific gravity, owing to the rather larger amount of mineral 
matter which it contains, by a higher softening or melting-point, 
and somewhat lower percentage of bitumen and, in consequence of 
these facts, a much greater hardness at all temperatures. 

Naturally the percentage of malthenes is smaller in the land 
than in the lake asphalt and that of fixed carbon slightly higher. 

The ultimate composition of the pure bitumen of land asphalt as 
compared with that of lake is given in the second table on page 177. 

The weathering of the bitumen has, therefore, produced essen- 
tial changes in the composition of the material, there having 
been a loss of sulphur, probably due to its elimination as hydro- 
gen sulphide, and an increase in carbon, due to the same cause 
and to the elimination of hydrogen as water during the process of 
condensation. 

These differences, though small in themselves, are indicative 
of the fact that the weathered land asphalt is not the same in 
its character as the fresh lake material. In themselves they 
would not amount to a great deal unless confirmed by actual 
results obtained in the use of the material industrially. As a 
matter of fact, such confirmation is not lacking if land is used in 
the same way as lake asphalt, that is to say, if fluxed to an asphalt 
cement with ordinary paraffine petroleum residuum. In the 
preparation of such an asphalt cement the striking differences 



176 



THE MODERN ASPHALT PAVEMENT. 
REFINED TRINIDAD LAND ASPHALT. 



Test number. 
Bitumen. . . . 



PHYSICAL PROPERTIES. 

F,/78° F., original sub- 



Specific gravity, 78' 

stance, dry 

Color of powder or streak 

Lustre 

Structure 

Fracture 



Odor 

Softens 

Flows 

Penetration at 78 c 



CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours 

Character of residue 



Loss, 400° F., 7 hours (fresh sample) 
Character of residue 



Bitumen soluble in CS 2 , air temperature. 

Difference 

Inorganic or mineral matter 



Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 
H 2 S0 4 

Per cent of total bitumen as saturated hy- 
drocarbons 



63260 
Lake R. A. 



1.40 

Blue-black 

Dull 

Homogeneous 

Semi- 

conchoidal 

Asphaltic 

180° F. 

190° F. 

7° 



1.1% 
Smooth 

4.0% 
Blistered 



Bitumen soluDie in 62° naphtha. 
This is per cent of total bitumen. 



Carbenes: 

Bitumen more soluble in carbon tetra- 
chloride, air temperature 



Bitumen yields on ignition: 
Fixed carbon 



Sulphur. 



56 .53% 

6.97 
36.50 



100.0 



35.6% 
63.1 

61.3 

24.4 

41.7% 
73.9 



1.3% 

10.8% 
6.2% 



36721 
Land R. A, 



1 .4196 
Brown-black 

Dull 

Homogeneous 

Semi- 

conchoidal 

Asphaltic 

188° F. 

198° F. 

0° 



1-0% 
Blistered 

3.0% 
Blistered 



54.1% 

7.9 
38.0 



100.0 



33.5% 
61.9 

64.8 

21.8 

38.2% 
70.6 



0.0% 

12.9% 
5.0% 



INDIVIDUAL ASPHALTS. 



177 



REFINED TRINIDAD LAND ASPHALT. 
COMPOSITION.) 



(EXTREMES IN 



PHYSICAL PROPERTIES. 

Specific gravitv. 78° F./78° F., original substance, 

dry 

Softens o 

Flews 



Flow in per cent of Trim dad lake = 100%, 

CHEMICAL CHARACTERISTICS. 

Bitumen soluble in CS 2 , air temperature. . 

Difference 

Inorganic or mineral matter 



Per cent of total bitumen soluble in 88° naphtha. 

air temperature 

Per cent of soluble bitumen removed by H 2 S0 4 . . 
Per cent of total bitumen soluble in 62° naphtha. 

Bitumen yields on ignition: 

Fixed carbon 




1.450 
220° F. 
230° F. 

15% 



52.0% 

9.5 
38.5 



100.0 

52.0 
64.8 
60.0 



14.0 



COMPARISON OF ULTIMATE COMPOSITION OF PURE 
BITUMEN, TRINIDAD LAND AND LAKE ASPHALT. 





Land. 


Lake. 


Carbon 


83.7 

10.8 

5.1 

0.5 


82.33 

10.69 

6.16 

0.81 


Hydrogen 


Sulphur 

Nitrogen 


100.1 


99.99 



between lake and land asphalt are brought out by the fact that 
where 20 pounds of a good parafhne residuum is sufficient to make 
a suitable asphalt cement when added to each 100 pounds of lake 
asphalt, as much as 30 or more pounds of the same residuum are 
required to make a cement of the same consistency with land 
asphalt. Extended experience with surfaces laid with these two 
asphalt cements has shown that after 3 or 4 years service the 
surface laid with the land asphalt begins to show signs of deterio- 
ration and often at even shorter periods. Our practical results, 
therefore, confirm those obtained in the laboratory even more 
strikingly than might be expected. 



178 THE MODERN ASPHALT PAVEMENT. 

Land asphalt, as has been seen, contains a very much weathered 
and hardened bitumen, much more hardened than one would be 
led to believe from mere analytical results and only shown by 
the necessity for the use of half as much again of flux in making a 
cement, and by the fact that when cylinders of the two asphalts 
of the same size are placed upon a corrugated brass plate and 
exposed to a high temperature, at an angle of 45°, the land asphalt 
flows from but 20 to 50 per cent as far in a given time as is the 
case with the lake asphalt. This is, of course, due to the absence 
of the softer hydrocarbons of the malthene series which, in the 
lake asphalt, are very susceptible to increase of temperature and 
consequently occasion the more rapid flow of the latter. The 
absence of these malthenes in a paving cement is a serious deficiency. 

The recent advent of the heavy asphaltic oils as fluxes makes 
it possible, however, to supply to a certain extent the deficiencies 
in the bitumen of land asphalt by the addition of a suitable amount 
of such flux, instead of producing the required softness with a 
great excess of paraffine residuum, thus forming an unbalanced 
cement. Pavements made with such an asphalt cement have 
been fairly satisfactory, but are, unfortunately, uneven in char- 
acter owing to the lack of uniformity of the original land asphalt, 
and to the large amount of skill which must be used in combining 
the different ingredients and to the care which the production of 
a uniform asphalt cement from such materials presents. 

Bermudez Asphalt. — The occurrence of a deposit of asphalt 
in what has been called the Bermudez " Pitch Lake," in the State 
of Sucre, formerly Bermudez, in Venezuela, Fig. 4, has been 
described by the author in another place as follows : x 

" From the mouth of the Orinoco, the northeastern coast of 
Venezuela, which faces Trinidad, is low and consists of vast man- 
grove swamps, through which run deep tidal estuaries. That por- 
tion forming part of the State of Bermudez extends inland for many 
miles. It lies on the opposite side of the Gulf of Paria from Trini- 
dad. About 30 miles in an air-line from the coast the asphalt 
deposit, known as the Bermudez Pitch Lake, is found at the point 
where a northern range of foot hills comes down to the swamp. 

1 On the Nature and Origin of Asphalt, Long Island City, N. Y., 1898 



INDIVIDUAL ASPHALTS. 179 

The Guanaco River, a branch of the San Juan, one of the large 
canos or estuaries of this region, at about 65 miles in its winding 
course, from its mouth, runs within 3 miles of the deposit, but 
it is 5 or 6 miles to a suitable wharfage site. On the other hand, 
towards the north a road runs to the hills and to the village of 
Guaryquen. These are the means of communication with the 
deposit. The so-called lake is situated between the edge of the 
swamp and the foot hills in what might be termed a savanna. It 
is an irregular-shaped surface with a width of about a mile and a 
half from north to south and about a mile east and west. Its area 
is a little more than 900 acres, and it is covered with vegetation, 
high rank grass, and shrubs, 1 to 8 feet high, with groves of large 
moriche palms, called morichales. One sees no dark expanse of 
pitch on approaching it as at the Trinidad pitch lake, and except 
at certain points where soft pitch is welling up, nothing of the 
kind can be found. The level of the surface of the deposit does 
not vary more than 2 feet and is largely the same as that of the 
surrounding swamps. In the rainy season it is mostly flooded 
and at all times very wet, so that any excavation will fill up with 
water. These conditions make it difficult to get about upon it 
or to excavate pitch easily. 

" It is readily seen that this deposit is a very different one from 
that in the pitch lake of Trinidad. It seems to be in fact merely an 
overflow of soft pitch from several springs over this large expanse 
of savanna and one which has not the depth or uniformity of that at 
Trinidad. 

" Being on a level with the mangrove swamps and with foot hills 
on its other side, any large amount of asphalt could hardly be held 
in position here, as in the old crater in Trinidad, but would burst 
out into the swamp and be lost, and, as far as borings have been 
made, they seem to indicate but a small depth anywhere as com- 
pared with that of the Trinidad lake. 

" At different points there is at most a depth of 7 feet of mate- 
rial, while the deepest part of the soft maltha is only 9 feet and 
the average of pitch below the soil and coke only 4 feet. At points 
there is not more than 2 feet of pitch, and in the morichales or 
palm groves it is often 5 feet below the surface. At several points, 



180 THE MODERN ASPHALT PAVEMENT. 

scattered over the surface, are areas of soft pitch, or pitch that 
is just exuding from springs* The largest area is about 7 acres 
in extent and of irregular shape* This has little or no vegetation 
upon it, and from the constant evolution of fresh pitch is raised 
several feet above the level of the rest of the deposit. This soft 
asphalt has become hardened at the edges, but when exposed 
to the sun is too soft to walk upon. The material is of the nature 
of a maltha and it is evidently the source of all the asphalt in the 
lake, from these exudations the pitch having spread in every 
direction, so that no great depth of pitch is found even at this point. 

" A careful examination of the surroundings shows that in 
one respect there is a resemblance between the point of evolution 
of the soft pitch at the Bermudez and at the Trinidad lakes. Gas 
is given cff in considerable quantities at both places, and in both 
cases consists partly, at least, of hydrogen sulphide. At the 
Bermudez lake I was unable to determine whether it was accom- 
panied by carbonic dioxide, but the odor of hydrogen sulphide 
was strong. 

" The consistency of the soft pitch at the centre of the Ber- 
mudez lake is much thinner than that of the Trinidad lake. It 
will run like a heavy tar and does not evolve gas in the same rapid 
way or harden as quickly after collection. It therefore does not 
retain the gas which is generated in it, nor does the deposit as a 
whole do so to the same extent as the Trinidad pitch. Where, 
however, the surface of the soft pitch has toughened by exposure 
to the sun and air and where gas is given off beneath it, it is often 
raised in dome-like protuberances, the beehives which were spoken 
of by early visitors to the Trinidad lake. These have a thin wall of 
pitch and are filled with gas which readily burns, and have been 
seen two feet or more in height and 18 inches in diameter. They 
are, of course, found only near the soft spots. 

" Although the pitch at the Bermudez lake is too soft to entangle 
and hold permanently the gas which is given off, where the pitch 
of medium consistency is covered with water it does not escape 
so readily, and thus often raises in the pools of water a mushroom- 
like growth of pitch by the reduction of the gravity of the mass 
from the included gases. These mushrooms correspond completely, 



INDIVIDUAL ASPHALTS. 181 

except in size, with those described by Manross as existing at the 
Trinidad lake when he visited it. It seems, therefore, that we 
have to-day several of the phenomena represented at the Venezue- 
lan lake which the hand of man has destroyed at Trinidad. 

" There is, however, no evidence of the same simultaneous 
boiling up of water with the fresh soft pitch that has been deter- 
mined at the Trinidad lake, but that there is none at all is not 
certain, as at the time I visited the locality heavy rains were fall- 
ing which prevented the detection of a small amount. It seems, 
however, improbable, as the soft pitch contains little or no water 
and the traces found in the samples collected are probably derived 
from rain. 

" Hardening of the Main Mass of Pitch. — The soft pitch, after 
it exudes at the centre of the Bermudez lake, undoubtedly hardens 
slowly on exposure, but the condition of the surface of the main 
mass, which is very hard and rough, and of the harder borders 
of the soft spots is due to other causes also. 

" The edges of the areas of soft asphalt are covered here and 
there with masses of glance pitch and with black and brittle cin- 
ders or coke, and which seem to have been produced from the 
maltha by fire. This is evidently the case, since the rank growth of 
grass which is very dry in the dry season is particularly adapted 
for a rapid and intense combustion. Such fires have been even 
recently started intentionally and accidentally and to them are 
due the condition of the present surface of the deposit and the 
character of much of the pitch. 

" The general surface of the lake is very irregular and hard. 
There are many very narrow and irregular channels or depres- 
sions from a few inches to 4 feet deep, filled with water, and not 
being easily distinguished, one often falls into them. At the foot 
of the growth of grass and shrubs are ridges of pitch mingled with 
soil and decayed vegetation, which have been plainly coked and 
hardened by fires of the nature which have been mentioned. When 
this hardened material which forms only a crust is removed, asphalt 
of a kind suitable for paving is found. The crust is from 1J to 
2 feet in depth and very firm, while the asphalt underneath would 
not begin to sustain the weight which that of the Trinidad pitch 



182 THE MODERN ASPHALT PAVEMENT. 

lake does easily. There are breaks in the crust here and there 
through which soft pitch exudes as has been described. 

" It appears, therefore, that the Bermudez deposit owes its 
existence to the exudation of a large quantity of soft maltha, 
which is still going on and which has spread over a great extent; 
that this has hardened spontaneously in the sun, and has also, 
by the action of fire, been converted over almost the entire sur- 
face into a cokey crust of some depth, beneath which the best 
material lies and that here and there are scattered masses of glance 
pitch produced in a similar way from less violent action of heat. 
There is no evidence of a general movement and mingling of the 
mass of this deposit in any way that would produce a uniformity 
of composition as seen in the Trinidad pitch lake, although there 
is a certain amount of gas evolved at the soft spots where maltha 
exudes and some gas cavities are found in the general mass of 
the pitch beneath the crust." 

The original Bermudez pitch, as it exudes at the soft spots, 
contains no mineral matter or water and is consequently an 
extremely pure bitumen. It has the following ultimate com- 
position: 

Carbon 82.88% 

Hydrogen 10 . 79 

Sulphur 5.87 

Nitrogen 75 

100.29 

As in the case of the bitumen of Trinidad asphalt, sulphur plays 
an important role in its composition, but in the asphalt as it is 
used commercially much of this sulphur has disappeared, having 
been evolved as hydrogen sulphide, the industrial material con- 
taining less than 4 per cent. 

Exposure of the soft maltha to the sun, after its evolution 
and chemical changes, hardens the material somewhat. The com- 
mercial supply has, however, been largely altered, owing to the 
fact that the rank vegetable growth which extends over the 900 
or 1000 acres of the deposit has frequently been set on fire, either 
accidentally or intentionally, with the production of such a degree 
of heat as to convert much of the material on the surface to coke 



INDIVIDUAL ASPHALTS. 



183 



and that below to a harder form of bitumen than that of the orig- 
inal maltha. It is. of course, very evident that this conversion 
has not been uniform and that the product taken from the lake 
cannot, on this account, be in itself uniform. In a collection of 
some forty samples taken in 1896, the following extremes of com- 
position were found: 



EXTREMES IN THE COMPOSITION OF CRUDE BERMUDEZ 

ASPHALT. 



CRUDE SUBSTANCE. 

Loss, 212° F., 4 days 

" 400° F., 7 hours. 

DRIED SUBSTANCE. 

Specific gravity, 78° F./78° F 

Loss, 400° F. f 7 hours 

Softens 

Flows 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Bitumen soluble, 88° naphtha, air temperature. 
This is per cent of total bitumen 




Lowest. 



10.72% 
4.72 



1.005 

5.81 
140° F. 
135° F. 

90.65% 
0.62 
0.50 

63.40 

67.78 



The asphalt as it occurs in the deposit holds from 46 to 10 per 
cent of water and 3.6 to .5 per cent of mineral matter. These 
substances as well as the undetermined material, amounting 
to from 6 to .6 per cent, must be adventitious, and are in part, at 
least, derived from the vegetation with which it comes in contact 
and, although some of the organic matter is due to the conversion 
of part of the bitumen to coke by fires, the greater portion con- 
sists of roots of grasses and shrubs which penetrate the asphalt 
with ease. 

The wide variation in the character of the material in differ- 
ent parts of the deposit is therefore made evident by the above 
figures. The high percentage of undetermined matter is not, as 
in Trinidad asphalt, due to the presence of clay or volatile inor- 
ganic salts. 

There are other evidences of this variation derived from the 



184 



THE MODERN ASPHALT PAVEMENT. 



examination of various cargoes of Bermudez asphalt which have 
been brought to this country for commercial use. 





Crude. 


After Drying. 


Year. 


Water. 


Bitumen 
Soluble 
in CS2. 


Difference 
Undeter- 
mined. 


Inorganic or 
Mineral 
Matter. 


1898 


.15.8% 
19.8 

23^9 
53.2 
29.9 
33.3 


95.7% 

92.5 

95.0 

95.7 

89.2 

97.0 

95.5 


2.3% 

4.3 

2.5 

2.8 

9.0 

1.5 

2.9 


2.0% 
3.0 


1899 


1901 


2.5 


i ono / Good sample 

1902 \Poor " 


1.5 

1.8 


1 ono f Good sample 


1.5 


1903 \ Poor " 


1.6 







Refined Bermudez Asphalt. — When the crude Bermudez asphalt, 
as it is taken from the deposit, is melted and dried it becomes the 
refined Bermudez asphalt of commerce and it is, of course, vari- 
able in character like the crude material it is derived from. The 
loss of light oils in the softer material has a tendency to bring all 
the refined asphalt more nearly to a uniform condition than would 
be expected. There are, however, decided differences not only 
as regards its physical characteristics but also chemically. 

The variation in the consistency is well shown by the relative 
length to which various lots of this asphalt will flow on an inclined 
plane at temperatures abov» the softening point. For several 
cargoes in this way the following data were obtained: 

PER CENT OF FLOW. 
Original material in use in Washington, D. C, 

1893 100.0% 

Importation of 1895 73.5 

" 1898 73.0 

" " March, 1899. . . 50.0 

" " May " 41.6 

" " June " 73.3 

" " 1903... 125.0 

From the preceding figures it appears that while the first mate- 
rial brought to this country was quite soft, the refined asphalt 
became harder in subsequent years and recently is again softer 



INDIVIDUAL ASPHALTS. 185 

owing to the fact that the crude asphalt has been collected of 
late at points nearer the maltha springs. 

In consequence of this every lot of Bermudez asphalt must be 
handled in its own Deculiar way, and in this respect it compares 
unfavorably with Trinidad lake asphalt which is, as has been 
seen, extremely uniform. 

The percentage of bitumen in the refined material varies as 
well as the consistency, ranging from 93 to 97 per cent, but will 
usually average 95 per cent. 

The data given in the tables on pages 186 and 187 show the 
physical properties and approximate chemical composition of refined 
Bermudez asphalt available on the market in 1900 and 1903. 

Bermudez asphalt is a comparatively pure bitumen and conse- 
quently possesses the lustre of such material instead of the dull 
fracture of Trinidad bitumen which is due to the presence of 
mineral matter. It has a uniform" structure with here and there 
small particles of vegetable organic matter. The fracture at low 
temperature is somewhat conchoidal and the consistency, as shown 
on the Bowen penetration machine, ranges from 22 to 26°. The 
specific gravity of the material is 1.08, somewhat higher than that 
of the pure bitumen of Trinidad asphalt, on account of the presence 
of a certain amount of mineral matter. The hydrocarbons compos- 
ing the bitumen consist to a very considerable extent of such as 
are volatile at 400° F., or even at 325° F. In this respect it is 
markedly different from Trinidad lake asphalt. Bermudez asphalt 
differs from Trinidad lake asphalt in containing a larger percent- 
age of maithenes, ' which accounts for its greater softness. As 
this percentage becomes increased the softer is the consistency 
of the asphalt, as appears from the fact that the softer refined 
material of 1903 contains 71.9 per cent of maithenes, where that 
of 1900 contained but 65.4 per cent. 

The percentage of saturated hydrocarbons unacted upon by 
sulphuric acid in Bermudez asphalt is about the same as that 
found in Trinidad lake asphalt, so that the bitumens in the two 
asphalts do not differ essentially in this respect. 

The undetermined matter not of a bituminous nature in Ber- 
mudez is, as a rule, very much smaller than in Trinidad asphalt and 



186 



THE MODERN ASPHALT PAVEMENT. 
REFINED BERMUDEZ ASPHALT. 



Test number. 



Year. 



PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Color of powder or streak 

Lustre 

Structure 

Fracture 



Hardness, original substance. 
Odor 



Softens 

Flows 

Penetration at 78° F. 



CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours 

Character of residue 



Loss, 400° F., 7 hours (fresh sample) 
Character of residue 



Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter. 



Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen. 

Per cent of soluble bitumen removed by 
H 2 S0 4 

Per cent of total bitumen as saturated hy- 
drocarbons 



Bitumen soluble in 62° naphtha. 
This is per cent of total bitumen. 



Carbenes: 

Per cent bitumen insoluble in carbon 
tetrachloride, air temperature 



Bitumen yields on ignition : 
Fixed carbon. 



Sulphur. 



44412 
1900 



1.0823 
Black 
Bright 
Uniform 
Semi- 
conchoidal 

Soft 

Asphaltic 

170° F. 

180° F. 

22° 



3.0% 
Smooth 

8.2% 
Wrinkled 

95.0% 
2.5 
2.5 



100.0 



62.2% 
65.4 

62.4 

24.4 

69.2% 
72.8 



0.1% 

13.4% 
4.0% 



67753 
1903 



1.0575 
Black 
Bright 
Uniform 
Semi- 
con choidal 

Soft 

Asphaltic 

1C0° F. 

170° F. 

26° 



4.4% 
Smooth 

95% 
Shrunken 

96.0% 
2.0 
2.0 



100.0 



69.1% 
71.9 

67.4 

23.4 

75.9% 
79.0 



1.1% 
14.0% 



INDIVIDUAL ASPHALTS. 



187 



EXTREMES IN THE COMPOSITION OF REFINED BERMUDEZ 

ASPHALT. 



PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance 

dry 

Flow in per cent of average 

CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours 

Loss, 400° F., 7 hours (fresh sample) 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Per cent total bitumen soluble in 88° naphtha 
air temperature 

Per cent total bitumen soluble in 62° naphtha. 

Bitumen yields on ignition : 

Fixed carbon 



14.0 



1.085 
41.6% 


1.057 

178%, 


5.5% 


1.5% 


9.5% 


4.5% 


93.0% 
5.0 
2.0 


96.8% 
1.4 
1.8 


100.0 


100.0 


65.0 


73.0 


72.0 


83.0 



13.5 



of an entirely different origin. In Bermudez asphalt it is derived 
almost entirely from vegetable organic matter in the shape of grasses 
and twigs with which the pitch has become contaminated. As a 
result of this, when the asphalt is made into a cement with a flux 
and maintained in a melted condition for a considerable period 
of time, this settles out on the bottom of the melting-tank as the 
gummy material whinh has been mentioned by the persons not 
further investigating its nature. If this gummy material is 
extracted with carbon disulphide, the vegetable nature of the 
material will be revealed at once. 

If the ultimate composition of the bitumen of Bermudez asphalt 
where it exudes into the lake and that of the pure Trinidad bitu- 
men are compared, it will be noticed that they agree very closely 
in their composition (see table, page 188). 

The percentage of fixed carbon which Bermudez refined asphalt 
yields on, ignition is much higher than that found in Trinidad 



188 



THE MODERN ASPHALT PAVEMENT 



COMPARISON OF ULTIMATE COMPOSITION OF PURE BITUMEN, 
BERMUDEZ AND TRINIDAD ASPHALT. 





Bermudez, 
Pure Bitumen. 


Trinidad, 
Pure Bitumen. 


Carbon i 


82.88% 
10.79 
5.87 
.75 


82.33% 
10.69 
6.16 
.81 


Hydrogen 


Sulphur 


Nitrogen 




100.29 


99.99 



asphalt and it is an amount which is usually characteristic of all 
the native bitumens which are distinctly asphaltic in their nature. 

The amount of sulphur is greater in the softer than in the 
harder varieties. 

From the preceding data the two most important asphalts 
in use in the paving industry may be compared with the following 
results: 

Trinidad asphalt is one which carries a very considerable amount 
of mineral matter which acts as a filler. Bermudez asphalt is a 
nearly pure bitumen. Trinidad asphalt is very stable at high 
temperatures and but little susceptible to change. Bermudez 
asphalt volatilizes an appreciable amount of light oils at high 
temperatures and hardens very rapidly. Bermudez asphalt con- 
tains a larger percentage of malthenes than Trinidad and on this 
account is more susceptible to temperature changes. Finally, 
Trinidad asphalt is a substance of fixed and extremely uniform 
composition, while Bermudez asphalt is most variable in this re- 
spect, material from different parts of the deposit showing great lack 
of uniformity in both its physical and chemical properties. The 
relative merits of the two materials from an industrial point of view 
will be considered later when surface mixtures are under discussion. 

Maracaibo Asphalt. — The asphalt used in the paving industry, 
known as Maracaibo asphalt, is put upon the market by the United 
States and Venezuela Company. It is found in the State of Zulia, 
west of the Gulf of Maracaibo, on the river Limon, about 50 miles 
west from the City of Maracaibo, as shown on the accompanying 
map, Fig. 5. The principal deposit is known as that o£ Inciarte. 



INDIVIDUAL ASPHALTS. 



189 



It is an exudation, from maltha springs, of 
gathered up and crudely refined, after which 
the river to the village of Toas, at the opening 
into the Gulf, from which point it is shipped to 
The material resembles and possesses many 
tics of the crude Bermudez asphalt, but it is 



bitumen which is 
it is floated down 
of Maracaibo Lake 
the United States, 
of the characteris- 
distinguished from 




Fig. 5. 

it by having a markedly rank odor suggestive of unsaturated 
hydrocarbons and of sulphur derivatives This odor may, how- 
ever, be due somewhat to cracking which has taken place during 
refining, since in the analysis of the material numbered 66923 
seventeen per cent of the bitumen is in the form of carbenes 
insoluble in cold carbon tetrachloride, while in the samples col- 
lected in 1904 less than two per cent is in this form. 

Five analyses of the crudely refined material made in the New 
^ork Testing Laboratory have resulted as follows: 



190 



THE MODERN ASPHALT PAVEMENT. 



MARACAIBO 



Test number 

Date sample received 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 

Color of powder or streak 

Lustre 

Structure. . . 

Fracture 

Hardness, original substance 

Odor 

Softens 

Flows 

Penetration at 78° F. 

CHEMICAL CHARACTERISTICS. 

Original substance: 

Loss, 212° F., 1 hour 

Dry substance: 

Loss, 325° F., 7 hours 

Character of residue 

Loss, 400° F. , 7 hours (fresh sample) 

Character of residue 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by H 2 S0 4 

Per cent of total bitumen as saturated hydrocarbons 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 

Bitumen yields on ignition : 

Fixed carbon , 

Vegetable organic matter. , 

1 Loss determined in open dish temperature 325° to 350* 



60380 
6-19-02 



1.0784 
Black 
Bright 
Uniform- 
homogeneous 
Semi- 
conchoidal 
1 
Strong 
280° F. 
300° F. 
8° 



Trace 



92.2% 
6.3 
1.5 


100.0 


45.8% 
49.7 


49.7% 
53.5 



19.0% 



INDIVIDUAL ASPHALTS. 



191 



ASPHALT. 



61047 


66923 


72214 


72215 


8-20-02 


10-19-03 


8-25-04 


8-25-04 


1.0634 

Black 

Bright 

Uniform. 


1.0638 

Black 

Bright 

Uniform 


1.0660 

Black 

Bright 

Uniform 


1.0621 
Black 
Bright 

Uniform 


Semi- 

conchoidal 

Soft 

Strong 

220° F. 

230° F. 

25° 


Semi- 
conchoidal 

Soft 
Strong 
200° F. 
210° F. 

20° 


Semi- 

conchoidal 

Soft 

Strong 

215° F. 

230° F. 

27° 


Semi- 

conchoidal 

Soft 

Strong 

195° F. 

210° F. 

26° 


Trace 


,3% 






4.5% « 


2.7% 
Blistered 


1-5% 
Smooth 


1.5% 
Smooth 




4.7% 
Much blistered 


5.8% 
Blistered 


6.0% 
Blistered 


94.0% 

4.5% 
1.5 


96.8% 
1.4 
1.8 


92.2% 
2.0 
5.8 


94.3% 
2.1 
3.6 


100.0 


100.0 


100.0 


100.0 


54.5% 
57.9 


45.7% 
47.2 
46.4 
25.3 


53.4% 
57.9 
48.5 
25.5 


53.9% 
57.2 
49.2 
29.1 


59.5% 
63.3 


51.5% 
53.2 






.... 


17.5% 2 


1.5% 


1-3% 


15.0% 


18.0% 


17.0% 


16.9% 




8.0% 







2 Duplicate 17.8%. 



192 THE MODERN ASPHALT PAVEMENT. 

It appears from the preceding data that Maracaibo ; asphalt , 
like that from the Bermudez lake, contains considerable vegetable 
organic matter. On re-refining in the laboratory it has a density 
corresponding to the pure bitumen of Trinidad lake asphalt, that 
is to say, somewhat less than that of Bermudez, and a very con- 
siderable degree of purity, from 92 to 97 per cent. The refined 
material is soft enough to be indented with the finger-nail. Apart 
from the preceding characteristics it differs in other respects from 
Bermudez asphalt and from other asphalts with which we are 
acquainted. Its softening-point is not only higher than that of 
Bermudez asphalt but even that of Trinidad. It contains a very 
small percentage of malthenes, which might be expected from its 
high softening-point, but not from its consistency. The percent- 
age of saturated hydrocarbons found in the malthenes is 25 to 
29 per cent. The percentage of fixed carbon obtained on ignition 
is higher than that found in the normal asphalts, reaching 18 per 
cent. On heating it to a temperature not above 325° F. gas is 
evolved showing that the bitumen is unstable and in a state of 
change. What effect these peculiarities may produce in the 
asphalt pavements constructed with it time and experience alone 
can tell. 

Cuban Asphalts. — Many different forms of native bitumens are 
found in the island of Cuba but the deposits are of such small 
extent in any one place that they are of no great commercial inter- 
est, except that they are imported in small amounts for the manu- 
facture of varnishes and in one or two instances for paving purposes. 
Solid bitumen, in the form of grahamite, has been mined in 
the Provinces of Pinar del Rio and Havana, but no attempts have 
been made to utilize these in the paving industry. In the neigh- 
borhood of the village of Bejucal, 18 miles south of Havana, there 
are several mines of bitumen of an asphaltic nature, one of which 
has been worked, on a commercial scale and utilized in the United 
States in the construction of pavements in Washington, D. C. The 
bitumen is more or less variable. A specimen of it had the follow- 
ing composition: 



INDIVIDUAL ASPHALTS. 193 

ASPHALT FROM BEJUCAL DISTRICT, CUBA. 

Test number 22220 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 .305 

Color of powder or streak Red-brown 

Lustre Dull 

Structure Compact 

Fracture Semi-conchoidal 

Hardness 2 

Odor Asphaltic 

Softens 230° F 

Flows 240° F 

Penetration at 78° F 0° 

CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours .88% 

Character of residue Cracked 

Loss, 400° F., 7 hours (fresh sample) 1 .50% 

Character of residue Wrinkled 

Bitumen soluble in CS 2 , air temperature 75. 1% 

Difference 3.5 

Inorganic or mineral matter 21.4 

lOOflO 

Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 32 . 4% 

This is per cent of total bitumen 43. 1 

Per cent of soluble bitumen removed by H 2 S0 4 60 . 5 

Per cent of total bitumen as saturated hydrocarbons 17.0 

Bitumen soluble in 62° naphtha 39.6% 

This is per cent of total bitumen 52 . 7 

Carbenes : 

Bitumen more soluble in carbon tetrachloride, air temper- 
ature 1 . 6% 

Bitumen yields on ignition: 

Fixed carbon 25.0% 

Sulphur 8.3% 



194 THE MODERN ASPHALT PAVEMENT. 

In general appearance the Bejucal asphalt resembles the Trini- 
dad refined material. It contains about 21 per cent of mineral 
matter in the form of silica and silicates and 75 per cent of bitumen. 
The specific gravity of the asphalt corresponds to a mixture of 
bitumen and mineral matter in these proportions. It has a very 
high softening point. The percentage of its total bitumen in the 
form of saturated hydrocarbons as revealed by the action of sul- 
phuric acid on the malthenes soluble in 88° naphtha is smaller 
than that in Trinidad asphalt. It contains a large percentage 
of sulphur and yields a high percentage of fixed carbon, larger 
than that usually found in any of the asphalts. In this respect 
it is more closely allied to the grahamites than to the asphalts, 
and it may perhaps eventually be necessary to classify it with 
the latter form of bitumen. As might be expected from its 
extreme hardness, the percentage of malthenes is only about two- 
thirds as much as that found in Trinidad and Bermudez asphalt, 
and this necessitates the use of a heavy asphaltic flux in the prepa- 
ration of a satisfactory asphalt cement from this material. 

In the neighborhood of the Bejucal mine are several others, 
partial examinations of which have been made giving the results 
tabulated on page 195. 

Mexican Asphalt. — Native bitumen in the shape of maltha 
and in a more or less solid form is of frequent occurrence in Mexico, 
especially along the coast of the Gulf of Mexico, in the States of 
Tamaulipas and Vera Cruz. In the neighborhood of Tampico 
and Tuxpan attempts have been made for many years to work 
the large effusions of maltha which occur there. At none of these 
deposits, however, is there a sufficient amount of bitumen avail- 
able to make the material of commercial importance. Lots of 
several hundred tons have, however, been collected and shipped 
to the United States and used in pavements, so that it may be 
a matter of interest to determine what the character of the bitu- 
men is. 

Asphalt Effusions on the Tamest River. — At about 45 miles from 
Tampico and 25 miles from Los Esteros, a station on the Me. 
& Gulf R.R., there are large tar springs. From these effusions 
some hundreds of tons of asphalt have been collected from time 



INDIVIDUAL ASPHALTS. 



195 



DEPOSITS IN THE NEIGHBORHOOD OF THE BEJUCAL 
MINE, CUBA. 



Test number 

Name of mine 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Color of powder or streak 

Lustre 

Structure 

Fracture 

Hardness, original substance 

Softens 

Flows 

Penetration at 78° F 

CHEMICAL CHARACTERISTICS. 

Original substance: 

Loss, 212° F., 1 hour 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter , 

Malthenes : 

Per cent of total bitumen soluble in 88° 
naphtha, air temperature 

Per cent of total bitumen soluble in 62° 
naphtha 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, 
air temperature 

Bitumen yields on ignition: 

Fixed carbon 





22221 


"Angelo 


"Raboul" 


Elmira" 




1.348 


1.306 


)ark brown 


Brown 


None 


None 


Uniform 


Brecciated 


Semi- 


Conchoidal 


conchoidal 




3 


2 


245° F. 


240° F. 


270° F. 


250° F. 


0° 


0° 



3.2% 



• 4% 



68.6% 

3.5 
27.9 


73.0% 
4.0 
23.0 


100.0 


100.0 


36.6% 


49.3% 





64.5% 





14.3% 


.... 


17.4% 



to time and shipped to the United States. The material is not ol 
uniform composition, samples collected in 1899 and examined in 
the author's laboratory having the characteristics given in the first 
table on page 196 and in the table on page 197. 

It appears that this bitumen although usually originally quite 
hard, as shown by the penetration at 78° F., loses a large amount 
of volatile matter on heating and becomes converted into a pitch 



196 



THUJ MUJJUKJN AS-fliA-LT PAVEMENT. 



FROM TAMESI RIVER, MEXICO. 

SAMPLES COLLECTED AT DEPOSIT. 



Test number 


28075 

99.5% 

0.0 

.5 


28076 

68.3% 

6.8 
24.9 


28077 

59.7% 

6.9 
33.4 


28078 


Bitumen soluble in CS 2 , air temp . . 
Difference 


68.1% 
2.4 


Inorganic or mineral matter 


29.5 


Loss, 230° F., until dry 

Loss, 325° F., 7 hours additional.. 
Loss, 400° F., 5 hours additional. . 


2.83% 
17.30 
8.42 


13.50% 
7.46 
3.36 


4.37% 
6.34 

2.42 


9.66% 
13.75 
9.68 


Residue after 325° and 400° 


Pitch 


Pitch 


Pitch 


Pitch 


Penetration of original material 
at 78° F 


25° 


40° 


25° 


57° 







in all cases. The instability of the material, as revealed by this 
fact, would necessitate the heating of this bitumen until all the 
volatile portion was removed before it could be used for paving 
purposes satisfactorily. For this reason, as well as on account 
of its great lack of uniformity and the small extent of the avail- 
able supply, it will not, probably, play a very important part in 
the asphalt paving industry. 

Deposits at Chijol. — At a locality known as Chijol, 25 miles 
from Tampico, on the Mex. Cent. R.R., and 3 miles distant from 
the latter, asphalt effusions have been worked to a limited extent. 
A sample of this material has the following characteristics: 

TEST NO. 28082. 

Loss, 250° F., until dry 12.70% 

Penetration at 78° F. (original substance) 66° 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 13.42% 

Residue after heating Pitch 

Loss, 400° F., 5 hours 7.24% 

Residue after heating Pitch 

Bitumen soluble in CS 2 , air temperature. ... 91 . 1% 

Difference 1.7 

Inorganic or mineral matter 7.2 

100.0 



INDIVIDUAL ASPHALTS. 



197 



FROM TAMESI RIVER, MEXICO. 

SAMPLES SHIPPED TO NEW YORK. 



Test number. 



Specific gravity, 78° F./78 F. (original). 

(dry) 

Flashes, °F 



Loss, 212° F., until dry. 



Loss on refining — water. . . . 
*' li " — impurities. 



Total loss 

Penetration of refined substance at 78° F. 

REFINED SUBSTANCE. 



3, 325° F., 7 hours 

Penetration of residue at 78° F. 



Loss, 400° F., 7 hours (fresh sample). . . 
Penetration of residue at 78° F 



Loss, 325° F., 21 hours. 
28 " 

Loss, 400° F., 21 hours. 
n a 28 " 



Bitumen soluble in CS a , air temperature . 

Difference 

Inorganic or mineral matter 



Malthenes : 

Bitumen soluble in 88° naphtha, air 

temperature 

This is per cent of total bitumen soluble. . 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen soluble. . 

Bitumen yields on ignition : 

Fixed carbon 



89.1% 
1.8 
9.1 



100.0 



49.5% 
55.6 

57.0% 
64.0 



16.1% 



44312 


51471 




1.211 


1.118 




15.0% 


20.1% 


15.0% 
8.0 


20.1% 
22.2 


23.0 


42.3% 


16° 


38° 


1.5% 
15° 


1.8% 


4.3% 
Pitch 


5.5% 
Pitch 




3.4% 



71.5% 

8.3 
20.2 



100.0 



48.8% 
68.2 

56.2% 
78.7 



10.4% 



51470 
1.0385 
308° F. 

10.0% 



4.8% 
70° 

8.9% 
50° 



10.4% 



16.9% 

99.0% 
.5 
.5 

100.0 



73.9% 
74.6 

83.8% 
84.6 



12.6% 



It will be noted that this bitumen is very similar to the purer 
form of that found along the Tamesi River; that is to say, it loses 
large quantities of volatile matter on heating and becomes con- 
verted into a pitch. For the same reasons, as in the case of the 
previous bitumen, it will not prove of any importance in the paving 



198 THE MODERN ASPHALT PAVEMENT. 

industry, although no doubt a certain proportion of both of these 
materials could be incorporated with other and more satisfactory- 
asphalts if it were a matter of economy to do so. 

Deposits in the Neighborhood of Tuxpan. — 54 miles from Tuxpan 
and 9 miles from the Tuxpan River are found large effusions of 
asphalt, identified under the name of the Santa Theresa deposits, 
attempts to develop which have been made for many years, and 
by many individuals, and with but little success from a com- 
mercial point of view. 

A sample of the material examined in the author's laboratory 
had the following characteristics: 

FROM DEPOSIT AT TUXPAN, MEXICO. 

Test No. 28083. 

Loss, 230° F., until dry 15.30% 

Penetration at 78° F. (original substance) .. . . 76° 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 12.48% 

Residue after heating Pitch 

Loss, 400° F., 5 hours additional 6 . 84% 

Residue after heating Pitch 

Bitumen soluble in CS 2 , air temperature ... 90 . 3% 

Difference 3.1 

Inorganic or mineral matter 6.6 

100.0 

This bitumen is, it will be seen, quite similar to those found 
near Tampico. 

Deposits at Chapapote. — Effusions of asphalt which are iden- 
tified under the above name occur 15 miles from Timberdar, the 
head of navigation of the Tuxpan River. These deposits have 
been worked by the Mexcian Asphalt Company, who packed the 
material in bags and made an effort to float it down the river. 
Some of the bitumen thus exported was examined by the author, 
giving the results tabulated on page 199. 

From these data it appears that both soft and hard bitu- 
men are found on the Chapapote Ranch, but that the former 
hardens very rapidly on heating, like other Mexican bitumens, 



INDIVIDUAL ASPHALTS. 
FROM DEPOSIT AT CHAPAPOTE, MEXICO. 



199 



Test number 

Specific gravity at 78° F./78° F. (original) 

(dry) 

Color 

Lustre 

Structure 

Fracture 

Hardness 

Fuses 

Softens 

Flows 

Penetration at 78° F. (dry) 

Loss, 220° F., 2 hours 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 

Residue after heating, penetration at 78° F 

Loss, 400° F., 7 hours (fresh sample) 

Residue after heating, penetration at 78° F. 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble in 88° napntha, air temperature 
This is per cent of total bitumen 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen 

Bitumen yields on ignition : 

Fixed carbon 



42226 



1.045 



140 c 



11.4% 



4.7% 
84° 

13.0% 
32° 

99.0% 

.4 



100.0 

74.1% 
74.8 

83.5% 
84.3 



13.3% 



28080 
1.0343 

Black 

Shining 
Massive 
Conchoidal 
2 + 
Readily 
258° F 
272° F 



99.2% 
.1 

.7 



100.0 



21.5% 



and becomes converted into a pitch. The material of this descrip- 
tion which has been imported into the United States has been 
used by mixing it with other more desirable asphalts, or, where 
used alone, has made a more or less unsatisfactory pavement. 

Malthas and solid bitumens from various other deposits in 
Mexico have been examined in the author's laboratory but the 
preceding are sufficient to illustrate the general character of the 
material found in that country. From information available it 
hardly seems possible that any of these deposits can ever furnish 



200 THE MODERN ASPHALT PAVEMENT. 

a reliable commercial supply. They have been mentioned in this 
place merely to bring out this fact and to show the character of 
the material that is available. 

La Patera, California, Asphalt. — In Santa Barbara County, Cali- 
fornia, and about 9^ miles in an air-line west of the City of Santa 
Barbara, a vein or intrusion of asphalt in the shales of that neigh- 
borhood was worked for several years in the early nineties. Its 
geologic environment has been described by Eldridge. 1 
The material was used in the production of an asphalt cement which 
attracted much attention at that time, and was known as Alca- 
traz XX. Although the vein is now exhausted and the mine 
abandoned the bitumen is of some interest as being typical and 
illustrative of the hardest type of asphalt. In its best days it 
never yielded more than 70 tons in a day and generally not more 
than 30 or 40, the entire production in the 5 years that it was 
worked being less than 30,000 tons. 

La Patera crude asphalt is a mixture of bitumen with the min- 
eral matter of the adjoining shale, which is composed of sand 
and clay. Its fracture resembles in some respects Trinidad lake 
asphalt, the material being filled with small gas cavities due to 
the imprisonment of gas which has been evolved at an early stage 
in the existence of the material in the same way that takes place 
in Trinidad pitch. It differs from the latter in being very hard 
and brittle, not softening below 250° F. Material taken from 
the mine in 1894 contained 59 per cent of bitumen but in 1896 
this fell to 55 per cent and in 1897 it had fallen to 49 per cent. 
The latter material had the physical properties and proximate 
composition given in the table on page 201. 

From these figures it appears that the density corresponds to 
the percentage of mineral matter and bitumen which it contains. 
As has already been said, the softening point is very high. It of 
course, being so hard a material, loses but little on heating for a 
length of time at high temperature. The percentage of malthenes 
is, of course, very low and corresponds to that found in the Cuban 
asphalt. The percentage of hydrocarbons unacted on by sulphuric 
acid is low, lower even than in the Bejucal, Cuban, bitumen, and 

1 The Asphalt and Bituminous Rock Deposits of the U. S., 1901, 442. 



INDIVIDUAL ASPHALTS. 201 

LA PATERA, CALIFORNIA, ASPHALT. 

Test number — . *...... 13541 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 . 3808 

Color of powder or streak Black 

Lustre Dull 

Structure Uniform 

Fracture Irregular 

Hardness, original substance 2 

Odor Asphalti* 

Softens 260° F 

Flows o 300° F 

Penetration at 78° F 0° 

CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 1.5% 

Character of residue Shrunke* . 

Loss, 400° F., 7 hours (fresh sample) 2.5% 

Character of residue Shrunken 

Bitumen soluble in CS 2 , air temperature 49 . 3% 

Difference 2.1 

Inorganic or mineral matter o 48 . 6 

100.0 

Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 21 . 6% 

This is per cent of total bitumen 43 . 8 

Per cent of soluble bitumen removed by H 2 S0 4 81 .4 

Per cent of total bitumen as saturated hydrocarbons 8.1 

Bitumen soluble in 62° naphtha 26 . 7% 

This is per cent of total bitumen 54 . 1 

Carbenes: 

Bitumen more soluble in carbon tetrachloride, air temperature 1 . 7% 

Bitumen yields on ignition: 

Fixed carbon 14.9% 

Sulphur 6.2% 

the lowest found in any asphalt. It yields about 15 per cent of 
fixed carbon on ignition and is, therefore, a true asphalt and in no 



202 THE MODERN ASPHALT PAVEMENT. 

way allied to the grahamites. The percentage of sulphur which 
it contains is the same as that found in Trinidad asphalt. 

An asphalt of this description can only be used in combination 
with a dense residuum of an asphaltic petroleum. In the early 
days of the Alcatraz Company attempts were made to produce a 
paving cement by combining La Patera asphalt with the natural 
maltha found in the Carpinteria sands. Pavements made with 
this material went to pieces very rapidly, and it is not difficult, 
in the light of our present knowledge, to explain why this was so. 
The Carpinteria maltha hardens and becomes a pitch very rapidly 
on heating, with the result that it is impossible to guarantee that 
an asphalt cement made with it should have a proper consistency 
in an asphalt surface. Later on a heavy asphaltic petroleum 
residuum obtained from a petroleum produced at Summerland 
was used with much more satisfactory results, and some excellent 
pavements were laid with a cement prepared in this way, but 
the proportion of the La Patera asphalt to the oil, 40 to 60, was 
so small that it could be better regarded as an amendment to 
qualities lacking in the oil rather than as an asphaltic cement per se. 

Asphalt on the More Ranch, Santa Barbara County, California. 
— This deposit of asphalt is of importance not on account of its size, 
but because the addition of perhaps a shovelful of it to each barrel 
of residual pitch from California petroleum has been used as a 
basis for the statement that the latter contains a native solid 
bitumen. The deposit is found on the seashore about 6 miles 
to the west of Santa Barbara. It has been described by Mr. J. D. 
Whitney in his report on the Geological Survey of California, 
Geology, I, 132, by Peckham in the American Jour, of Science, 
(2), 48, 368, and by Eldridge. 

The shore here consists of an exposed cliff, 75 to 80 feet high, 
of sandy clay which is quite soft and easily weathered. It is 
much fissured and in these fissures the asphalt is found either 
in the shape of kidneys or veins. It can be seen at various points 
along the face of the cliff, where it has been exposed by the action 
of the waves. In places the wall rock is mixed in in fragments 
with the bitumen and in others it is a homogeneous material. 
The amount of bitumen found at any point is, therefore, very 



INDIVIDUAL ASPHALTS. 



203 



variable, as can be seen from the accompanying analyses. A few 
hundred tons have been taken out annually for many years and 
sold along the Pacific Coast. When the author examined the 
deposit in 1897 a kidney was being worked about 15 feet deep 
and about 12 feet broad, which illustrated the appearances of the 
material; larger masses than this are seldom found. It is evi- 
dent, therefore, that the asphalt available at this point is not of 
commercial importance. The composition of the material is as 
follows: 

ANALYSES OF ASPHALT FROM MORE RANCH, SANTA 
BARBARA COUNTY, CALIFORNIA. 

Test No. 13383. From mine, collected December, 1897. 
" " 13536. Supply ready for shipment on wharf. 
" " 13539. Stringer in tunnel from pit. 



DRY SUBSTANCE. 

Test number 

Bitumen by CS 21 air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Per cent of total bitumen soluble in 88 
naphtha , air temperature 

Loss of crude at 212° F., 1 hour 



13383 


13536 


38.3% 

3.4 
58.3 


40.1% 

1.4 
58.5 


100.0 


100.0 


63.2 


63.3 


•7% 


1.4% 



13539 

48.3% 

1.2 
50.5 

100.0 



59.2 

1.4% 



It is evident that the asphalt contains too little bitumen to 
melt readily without the aid of a flux. The pure bitumen extracted 
from the asphalt is much harder than that obtained from Trinidad 
lake asphalt, flowing but 69 per cent as far as the latter on a cor- 
rugated plate at high temperature. 

All attempts to utilize this material, except locally, have been 
made purely for advertising purposes in connection with the use 
of residual pitches, where specifications demanded the use of a 
native solid bitumen. 

Standard Asphalt. — In the western part of Kern County, in 
the first tier of foot-hills on the coast range, forming the western 
boundary of the central valley of California, at a point called 



204 



THE MODERN ASPHALT PAVEMENT. 



Asphalto, at the end of a branch of the Southern Pacific Railroad 
from Bakersfield, an asphalt mine was in existence in the nineties 
which was worked by the Standard Asphalt Company of Cali- 
fornia. The company originally endeavored to work certain 
superficial overflows of bitumen upon the surface of the ground, 
but the material proving to be of no value a shaft was sunk upon 
a vein which penetrated the shales at this point, in the manner 
which has been described by Eldridge. 1 Some of the material 
was obtained also by running tunnels. It is of interest in this 
place merely to determine the character of the bitumen which 
was obtained. 

The crude material was found in different degrees of purity 
and containing from 54 to 91 per cent of bitumen, as appears 
from the following analyses: 



FROM DEPOSIT OF STANDARD ASPHALT COMPANY, CALIFORNIA. 



Test number 

Bitumen bv CS„ air temperature . 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble in 88° naphtha, 

air temperature 

This is per cent of total bitumen . 

Loss of crude at 212° F for 1 hour 

Bitumen yields on ignition : 

Fixed carbon 



13391 

80.6% 
7.7 
11.7 

100.0 



46.0 
57.1 



7.3 



13589 
No. 1 
90.5% 

0.0 

9.5 



100.0 



49.8% 
55.0 

5.7% 



13589 
No. 2 
87.9% 

3.1 

9.0 



100.0 



43.1% 
49.0 

14.9% 



13593 

54.3% 

6.2 
39.5 



100.0 



31.0% 
57.1 

5.8% 



13594 

78.7% 
4.0 
17.3 



100.0 



41.0% 
52.8 

5.9% 



The crude material was a compact homogeneous brownish 
bitumen, very much resembling gilsonite in its outward appear- 
ance, but being very much softer. Much of it, although showing 
no outward evidence of so doing, contained an appreciable per 
cent of water which, together • with a certain amount of gas, is 
evolved on heating to 100° C. In some cases the loss reached 



The Asphalt and Bituminous Rock Deposits of the United States, 1901, 



449. 



INDIVIDUAL ASPHALTS. 



205 



REFINED STANDARD ASPHALT, CALIFORNIA. 

Test number 13601 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 .0627 

Color of powder or streak Black 

Lustre Dull 

Structure Uniform 

Fracture Semi-conchoidal 

Hardness Soft 

Odor Asphaltic 

Softens ". 170° F. 

Flows 180° F. 

Penetration at 78° F.. to 27° 

CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 6.6% 

Character of residue , Smooth 

Loss, 400° F., 7 hours (fresh sample) 19.9% 

Character of residue Blistered 

Bitumen soluble in CS, air temperature 89 . 8% 

Difference 3.4 

Inorganic or mineral matter 6.8 

100.0 
Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 53 .4% 

This is per cent of total bitumen 59 . 4 

Per cent of soluble bitumen removed by H 2 S0 4 51 .9 

Per cent of total bitumen as saturated hydrocarbons. .... 28 . 6 

Bitumen soluble in 62° naphtha 60 .0% 

This is per cent of total bitumen 66 . 8 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 0.3% 

Bitumen yields on ignition : 

Fixed carbon 8.0% 



as high as 16 per cent. The run of the mine would average above 
80 per cent of bitumen with 10 per cent of mineral matter and 
5 per cent of moisture and gas. This bitumen is more particu- 



206 THE MODERN ASPHALT PAVEMENT. 

larly characterized and differentiated from ordinary asphalts by 
the fact that it yields only 7 to 8 per cent of fixed carbon, where 
the asphalts and gilsonite contain 14 to 15 per cent. 

For the purpose of preparing the crude material for use in 
the paving industry it was melted with the addition of about 30 
per cent of a dense asphaltic flux. The resulting product was 
quite hard and was further fluxed for the purpose of making an 
asphalt cement. This material was in use to a considerable extent 
in the middle West before 1900, but the mine became exhausted 
and it is no longer available. 

The refined material had the characteristics tabulated on p. 205. 

The refined Standard asphalt was a rather pure bitumen carry- 
ing but 6.8 per cent of mineral matter with 90 per cent of bitu- 
men. The percentage of malthenes was smaller than that found 
in Trinidad and Bermudez asphalts, but the softening point was 
lower than would have been expected in such a case. As has 
been said the fixed carbon which this material yields is very low. 
Except for this its general outward resemblance to gilsonite would 
seem to point to the fact that the bitumen from the Standard 
mine must be closely allied to it. It differs from it, however, 
in that in gilsonite the percentage of the total bitumens present 
as saturated hydrocarbons is very much smaller. This may be 
due, however, to the fact that in gilsonite metamorphism has gone 
much further than in the case of the bitumen from the Standard 
mine. Although none of this bitumen is available for paving 
purposes at the present day, its character has been shown 
because of its uniform structure and resemblance in certain 
respects to gilsonite. 

Good pavements were constructed with the Standard bitumen 
where it was properly handled, but in many cases the surface 
failed to give satisfaction owing to lack of skill in its use. 

Other Deposits of Solid Bitumen in California. — In addition 
to the two abandoned deposits of asphalt which have been described, 
namely, those at the La Patera and Standard mines, there are 
numerous others scattered throughout Lower California, descrip- 
tions of which will be found in the Eldridge report on "The Asphalt 
and Bituminous Rock Deposits of the United States." None of 



INDIVIDUAL ASPHALTS. 207 

them have proved, although development has been attempted in 
many cases, to be of the slightest commercial importance, as the 
material available at any one point is too small to pay for mining 
it, owing to the fact that the bitumen is found in fissures or veins 
in the shales, which always pinch out at a very moderate depth, 
due to the pressure exerted by the superimposed strata, and is 
often mixed with such a large proportion of the mineral matter 
from the vein walls, at times in the shape of brecciated masses 
scattered through the bitumen, that it is extremely difficult to 
handle. The only interest to the paving industry in these deposits 
lies in the fact that minute percentages of them have at times 
been added to the solid residues from asphaltic oils in order to 
substantiate the claim that the latter contained native solid bitu- 
mens. As a paving material none of them has ever amounted 
to anything nor will any of them ever do so. 

SUMMARY. 

In the preceding pages the characteristics of the asphalts which 
are or have been available to any commercial extent are given. 
The supply of Trinidad asphalt is extremely large in amount, 
uniform in character, and much more stable than any other, owing 
to the character of the hydrocarbons of which it is composed. 
Bermudez asphalt, for the same reason, is much more liable to 
change. Maracaibo asphalt differs essentially from all others in 
several respects. The data in regard to many minor deposits 
illustrate the very considerable variation which occurs in material 
included under the specific designation asphalt. 



CHAPTER XI. 
SOLID NATIVE BITUMENS WHICH ARE NOT ASPHALT. 

It appears in our classification of native bitumens that several 
solid native bitumens exist which, from their peculiar character- 
istics, cannot be included among the asphalts. These include 
gilsonite, grahamite, manjak, and glance pitch. The two former 
are the only ones which are of any interest in the paving industry. 

Gilsonite. — The occurrence of gilsonite in Utah and Colorado 
is thoroughly described in the report of Eldridge, which has been 
frequently referred to. It is only necessary in the present place 
to consider its physical properties and proximate chemical com- 
position. 

Gilsonite is one of, if not the purest, forms of solid bitumen 
found in nature. It is practically entirely soluble in carbon di- 
sulphide. It varies to a certain extent in hardness in the various 
deposits and veins in which it occurs. The extremes in composi- 
tion in the present commercial supply appear in the following 
table. 

GILSONITE. 

PHYSICAL PROPERTIES. 



Test number 

Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Color of powder or streak 

Lustre 

Structure 

b racture 

liardness, original substance 

Softens 

Flows 

Penetration at 78° F 



92603 



80343 



1.044 


1.049 


Brown 


Brown 


Lustrous 


Lustrous 


Homogeneous 


Homogeneous 


Sub-conchoidal 


Sub-conchoidaj 


2 


2 


260° F. 


300° F. 


275° F. 


325° F. 









208 



SOLID NATIVE BITUMENS, NOT ASPHALT. 

CHEMICAL CHARACTERISTICS. 



209 



Dry substance: 

Loss, 325° F., 7 hours 

Character of residue 

Loss, 400° F., 7 hours , 

Character of residue , 

Bitumen soluble in CS 2 , air temperature . . . 

Inorganic or mineral matter 

Difference 

Malthenes : 

Bitumen soluble in 88° naphtha, air temp. 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 

H 2 S0 4 

Per cent of total bitumen as saturated 
hydrocarbons 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, 
air temperature 

Bitumen yields on ignition: 

Fixed carbon 



.9% 
Smooth 


2.3% 
Intumesces 


1.2 

Smooth 


4.0 
Intumesces 


99.0% 

.0 

1.0 


99.9% 
.1 
.0 


100.0 

47.2 

47.7 ' 


100.0 
15.9% 
15.9 


87.7 


71.8 


5.9 


4.5 


67.4% 
68.1 


30.3% 
30.4 


.0% 


•4% 


13.0% 


13.4% 



Gilsonite is known in the trade in two forms, firsts and seconds, 
the firsts being the highest-grade material in large lumps unac- 
companied by powder, while the seconds are that part of the 
mineral which occurs nearest the vein walls, and in fragmentary 
particles and are made up of the less attractive product of the 
mine. The difference in these two grades of gilsonite is one largely 
of appearance rather than quality when taken from the same vein. 

Gilsonite is the purest native bitumen with which we are 
acquainted, the best varieties containing 99.5 per cent of bitumen, 
and with but traces of matter not of a bituminous nature. The 
bitumen is equally soluble in cold carbon tetrachloride and carbon 
disulphide, thus differentiating it from grahamite and some of 
the residual pitches. 

Gilsonite is more variable when taken from different deposits 
and at different depths. 



210 THE MODERN ASPHALT PAVEMENT. 

The density of this bitumen is somewhat smaller than that 
of the asphalts and it has a much higher softening point, as might 
be expected from the fact that it is brittle and readily reduced 
to a reddish-brown powder, the latter characteristic alone differ- 
entiating it from the other native bitumens which give a 
much blacker powder. As would be expected in such a brittle 
material the percentage of malthenes is low, only 48 per cent 
of the total bitumen being soluble in 88° naphtha. The amount 
will vary, however, in gilsonite from different veins and from 
different parts of the vein, weathered material at times contain- 
ing but 14 per cent, while in the best it may rise to over 70 per 
cent. 

The hydrocarbons composing the malthenes of gilsonite are 
entirely different in character from those found in the asphalts. 
They are almost entirely composed of unsaturated hydrocarbons 
attacked by strong sulphurs acid, and this fact differentiates gil- 
sonite completely from asphalt. The hydrocarbons unattacked by 
dilute sulphuric acid are extremely viscous, sticky, and resinous 
and absolutely different from those found in any other native bitu- 
men, and there seems to be good ground for the inference that the 
other hydrocarbons composing gilsonite are likewise quite different 
from those occurring in the asphalts. A close study of these 
hydrocarbons will be of great interest, but our information at 
present available is sufficient to justify us in placing gilsonite 
in a class by itself among the native bitumens. Gilsonite is char- 
acterized by yielding the same percentage of fixed carbon on 
ignition that is found in the asphalts. This is not what would be 
expected from a consideration of the proximate composition of 
the material, which would lead us to suppose that the percentage 
would be higher. In material which is much weathered a higher 
percentage is actually found, reaching in one instance 26 per 
cent, and corresponding, of course, to a smaller percentage of 
naphtha soluble bitumen in the material, although the relation 
between fixed carbon and malthenes is by no means a constant 
one. Gilsonite is readily soluble in the heavy asphaltic residues 
from California and Texas petroleums and, when mixed with 



SOLID NATIVE BITUMENS, NOT ASPHALT. 21 1 

this in the proper proportion, makes a material which is extremely 
rubbery and more or less elastic and ductile. 

Gilsonite in the Paving Industry. — Gilsonite has been used 
very successfully and to a very considerable extent in the paving 
industry, the peculiar rubbery nature of the cement produced 
from it with a heavy asphaltic flux, and the fact that this cement 
is less susceptible to temperature changes than those made with 
the ordinary asphalts, making it a very desirable material. It 
was not available for use, at least in the East, until the advent 
of the Texas asphaltic flux in 1902, as the parafnne fluxes will 
not cut Gilsonite satisfactorily, the result being a very short 
and granular substance which has no cementing power, while 
the California fluxes were too expensive. Gilsonite has wide 
applications in many industries. Successful pavements have been 
laid with it which have been in use for years, and it is an impor- 
tant constituent of varnishes, insulations, and waterproofing com- 
pounds. 

Grahamite. — Grahamite is a brittle black bitumen, rarely of 
compact structure, which does not melt readily but merely intu- 
mesces on heating to high temperatures. It occurs in veins rather 
widely disseminated, but never in large amounts. Its physical 
properties and chemical constitution differentiate it from all 
other solid bitumens. Its structure is distinguished by what 
has been called a hackly or pencillated fracture produced appar- 
ently by the working of the brittle bitumen, induced by the move- 
ment of the vein wall. At times there is a grosser columnar 
structure. As types of this material, that found in Oklahoma 
in the Ten Mile Creek district, in the Choctaw Nation, and in 
Ritchie County, West Virginia, where it was originally discovered, 
will serve. These characteristics are shown by the analyses 
given on page 212. 

Grahamite is an almost entirely pure bitumen soluble in carbon 
disulphide, naphthalene, and dead oil, but it is differentiated from 
the asphalts and gilsonite by the fact that it is almost entirely insol- 
uble in naphtha, even of 62° density, and to the extent of 55.0 per 



212 



THE MODERN ASPHALT PAVEMENT. 



GRAHAMITE. 



Test number. 
Location .... 



PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F„, original sub- 
stance, dry 

Color of powder or streak 

Lustre 

Structure 



Fracture 

Hardness, original substance . 

Odor 

Softens 

Flows 

Penetration at 78° F 



CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours. 

Loss, 400° F., 7 hours (fresh sample). . 

Bitumen soluble in CS 2 , air temperature . 

Difference 

Inorganic or mineral matter 



Malthenes : 

Bitumen soluble in 88° naphtha, air temp 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 

H 2 S0 4 

Per cent of total bitumen as saturated 
hydrocarbons 



Bitumen soluble in 62° naphtha. 
This is per cent of total bitumen. 



Carbenes: 

Bitumen insoluble in carbon tetrachloride, 
air temperature 

Bitumen insoluble in hot carbon tetra- 
chloride 

Bitumen yields on ignition: 

Fixed carbon 



Ultimate composition: 

Carbon 

Hydrogen 

Sulphur 



Difference. 



68940 
Oklahoma 



1.171 

Black 

DuU 

Uniform 

Hackly 

Brittle 

None 

Intumesces 



+ .1% 

+ .5% 

94.1% 

.2 

5.7 

100.0 

.4% 
.4 

25.0 

.32 

.7% 
.7 



68.7% 
48.6 

53.3% 



75637 

West 
Virginia 



1.137 

Black 

Dull 
Uniform 

friable 

Irregular 

2 

None 

Intumescea 
it 

0° 



97.8% 

2^1 

100.0 

3.3% 
3.37 



3.4% 
3.47 



55.0% 
1.3% 

41.0% 

86.56% 
8.68 
1.79 
2.97 

100.00 



SOLID NATIVE BITUMENS, NOT ASPHALT. 213 

cent to 80.6 per cent in cold carbon tetrachloride. It is also differ- 
entiated from the asphalts and gilsonites by the fact that it yields 
from 30 to 50 per cent of fixed carbon on ignition. Grahamite, 
although not soluble in the lighter oils, is readily dissolved by 
the denser or semi-asphaltic fluxes, and in this condition forms a 
rubbery material quite similar to that produced in the same way 
with gilsonite. A small cylinder of it when bent upon itself will 
rapidly return to its original form. It lacks ductility, that is to 
say, it is very short when a cylinder of it is drawn out. 

A similar deposit of grahamite is found in Middle Park, Colo- 
rado. This material is inaccessible and of no commercial impor- 
tance. It has the composition given on page 214. 

It is apparent from the results of the analyses of the 3 gra- 
hamites that the different deposits vary in the degree to which 
the molecule has been condensed, as shown by the percentage 
of bitumen insoluble in cold carbon tetrachloride. 

It has also been found that grahamite can be divided into 
two classes, those containing sulphur and those containing oxygen. 

As has been said, numerous deposits of grahamite are found 
in Cuba, Mexico, Trinidad, and elsewhere, but they are of no 
commercial importance as far as the asphalt paving industry is 
concerned, although of great interest from a purely scientific 
point of view. These will be described by the writer in another 
place. 

Grahamite has a number of industrial uses. Successful pave- 
ments have been constructed with it in combination with gilsonite 
and heavy asphaltic fluxes. Mastic made with it is more resistant 
to grease and oil than the ordinary type, and it has been made 
a constituent of varnishes, of rubber substitutes, and of filler 
for brick and stone blocks. When cut with heavy asphaltic flux 
it is even more rubbery and elastic than gilsonite under the same 
circumstances, and less susceptible to heat. 

Glance Pitch and Manjak. — These bitumens are of little or 
no interest in connection with the paving industry, but they must 
be mentioned here in order to complete our description of the 
solid native bitumens. 

Glance pitch is a material which is quite widely distributed 



214 THE MODERN ASPHALT PAVEMENT. 

GRAHAMITE FROM MIDDLE PARK, COLORADO. 

Test number 19162 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 .160 

Color of powder or streak Black 

Lustre Dull 

Structure Uniform- 
homogeneous 

Fracture Columnar, 

scaly 

Hardness, original substance 3 

Odor None 

Softens Intumesces 

Flows " 

Penetration at 78° F 0° 

CHEMICAL CHARACTERISTICS. 

Bitumen soluble in CS 2 , air temperature 98 . 2% 

Difference 1.7 

Inorganic or mineral matter .1 

100.0 

Malthenes : 

Per cent total bitumen soluble in 88° naphtha, air tem- 
perature . 8% 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 80 . 6% 

Bitumen yields on ignition* 

Fixed carbon 47 .4% 

Ultimate composition: 

Carbon 85.97% 

Hydrogen 7 . 65 

Sulphur .93 

Difference (oxygen?) 5. 45 

100.00 



over the world, although the best supplies come from the East, 
Syria, and the Dead Sea. 

Manjak is found only in the island of Barbadoes. A bitumen 
is shipped from Trinidad under the name of manjak, but this 



SOLID NATIVE BITUMENS, NOT ASPHALT. 215 

material is really a grahamite and not a true manjak, as it does 
not melt and has all the properties of the latter bitumen. 

The characteristics of these materials are shown by the follow- 
ing analyses: 

EGYPTIAN GLANCE PITCH. 

Test number 14145 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 .097 

Color of powder or streak Black 

Lustre Lustrous 

Structure Brittle- 
uniform 

Fracture Conchoidal 

Hardness, original substance 2 

Softens 250° F. 

Flows 260° F. 

Penetration at 78° F 0° 

CHEMICAL CHARACTERISTICS 

Bitumen soluble in CS a , air temperature 99 . 7% 

Difference .2 

Inorganic or mineral matter. .1 

100.0 

Malthenes: 

Bitumen soluble in 88° naphtha, air temperature 23 . 5% 

This is per cent of total bitumen 23 . 6 

Per cent of soluble bitumen removed by H-jSO^ 72 .0 

Bitumen soluble in 62° naphtha , 36 . 9% 

This is per cent of total bitumen 37.0 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 0.1% 

Bitumen yields on ignition : 

Fixed carbon 15.0% 

Ultimate composition: 

Sulphur 8 . 52% 

Carbon 80 . 87 

Hydrogen 10.42 

Nitrogen .19 

100.00 



216 THE MODERN ASPHALT PAVEMENT. 

BARBADOES MANJAK. 
Test number 14143 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 .0844 

Color of powder or streak «• Dark brown 

Lustre Lustrous 

Structure Uniform 

Fracture Conchoidal 

Hardness, original substance 1 

Softens 230° F. 

Flows 250° F. 

Penetration at 78° F 0° 

CHEMICAL CHARACTERISTICS. 

Bitumen soluble in CS 2 , air temperature 99 . 2% 

Difference .5 

Inorganic or mineral matter .3 

100.0 

Malthenes: 

Bitumen soluble in 88° naphtha, air temperature 26 . 9% 

This is per cent of total bitumen 27 .0 

Per cent of soluble bitumen removed by H^S0 4 75 . 

Bitumen soluble in 62° naphtha 40 .4% 

This is per cent of total bitumen 40 . 7 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 1.2% 

Bitumen yields on ignition : 

Fixed carbon 25 .0 

It will be noted that glance pitch is a very brittle material, 
of a higher density and much higher melting-point than asphalt, 
of great purity and containing but a very small percentage of 
malthenes. It has evidently originated in the very complete 
hardening of asphalt either by natural causes or, exceptionally, 
by its exposure to heat in one way or another. 

Manjak resembles it in many respects, but is distinguished 
from it by being more closely related to grahamite, on account 
of the higher percentage of fixed carbon which it contains, that 
obtained from glance pitch being an amount normal to asphalt. 



SOLID NATIVE BITUMENS, NOT ASPHALT. 217 

while that from manjak approaches that obtained from grahamite. 
It is, however, differentiated from grahamite by the fact that it 
actually melts, instead of intumescing only, and dissolves com- 
pletely in cold carbon tetrachloride. 

In both of these solid bitumens there is a very small propor- 
tion of stable hydrocarbons unattacked by sulphuric acid. 

Ozocerite. — Ozocerite is a solid bitumen the principal supply 
of which is fouud in Galicia. A small amount of it is also found 
in Utah, in Emery and Uintah Counties. The hydrocarbons of 
which it is composed are solids, resembling paraffine scale. When 
purified it is known as ceresin and is used for the adulteration of 
beeswax, and as a substitute for paraffine scale, which it is superior 
to on account of its high melting-point. As it is a paraffine com- 
pound it is of no interest in the paving industry. 

Pyrobitumens. 

Albertite. — Albertite is an extremely brittle and lustrous 
material. It was first described by Wetherill. 1 It " occurs fill- 
ing an irregular fissure in rocks of the Subcarboniferous Age in 
Nova Scotia. 7 ' It has since been found in Cuba, Mexico, Okla- 
homa, and Utah. It is not a true bitumen, but a very small 
part of it being soluble in the usual solvents for that substance. 
It yields a very high percentage of fixed carbon. Analyses of 
albertites from various localities which have been examined in 
the author's laboratory are tabulated on pages 218, 219. 

Its ultimate composition is, for the Nova Scotia material, 

Carbon * 85.53% 

Hydrogen 13.20 

Sulphur 1 .20 

Nitrogen 42 

Albeitite is usually quite free from mineral matter, but in the 
case of that found in Mexico it contains 22.6 per cent and a rather 
larger portion of bitumen soluble in carbon disulphide than in 
that found elsewhere. 

The material is of no importance in the paving industry. 



Trans. Am. Phil. Soc, Phila., 1852, 353. 



218 



THE MODERN ASPHALT PAVEMENT. 



ANALYSES OF 



Locality. . . . 
Test number. 



PHYSICAL PROPERTIES. 



Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Color 



Lustre , 



Structure. 
Fracture. 



Hardness, original substance 

Odor 

Softens 



Flows 

Penetration at 78° F. 



CHEMICAL CHARACTERISTICS. 



Original substance: 

Loss, 212° F., until dry. 



Dry substance : 

Bitumen soluble in CS 2 , air temperature. 

Difference 

Inorganic or mineral matter. 



Malthenes: 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen 

Bitumen yields on ignition : 
Fixed carbon 



Sulphur. 



Nova Scotia 
L486 7834 



BlaclP 

Lustrous 

Homogeneous 
Smooth 



None 
Intumesces 



9.0% 
91.0 
.2 



100.2 



39.0% 



1.075 
Black 

Lustrous 

Homogeneous 
Smooth 



None 
Intumesces 



5.9% 
94.1 
.0 

100.0 



1.5% 



29.8% 

1.2% 



Wurtzilite. — Wurtzilite is a hard lustrous pyrobitumen, 
slightly elastic in thin fragments, which is found in Uintah County, 
Utah. It does not fuse at high temperatures, but a process has 
been devised for fluxing it with heavy malthas by gradually crack- 
ing it at high temperatures. It is practically insoluble in car- 
bon disulphicle and heavy residuum. 



SOLID NATIVE BITUMENS, NOT ASPHALT. 
ALBERTITE. 



219 



Utah. 


Utah. 


Mexico. 


Cuba. 


Oklahoma. 


19187 


30495 


36326 


62989 


74995 
Bright 
sample 


74995 

DuU 

sample 


1.092 


1.099 




1.204 






Black 


Brown- 
black 


Black 


Black 






Partly 


Partly 


DuU 


Lustrous 






lustrous 


lustrous 


Homogeneous 








Irregular 


Irregular 


Irregular 


Semi- 
conchoidal 






Brittle 


2 


2 


2 






None 


None 


None 


None 






Does not 


Intumesces 


Intumesces 


Intumesces 






intumesce 














n 


<« 


tt 






0° 


0° 


0° 


0° 








2.25% 


.2% 


.1% 






5.6% 


3.4% 


11.9% 


Trace 


1.6% 


6.8% 


94.2 


96.4 


61.9 


98.9% 


87.7 


71.2 


.2 


.2 


26.2 


1.1 


10.7 


22.0 


100.0 


100.0 


100.0 


100.0 


100.0 


100.0 




Trace 


3.2% 
23.4 




.0% 


•0% 


37.0% 


40.4% 


39.0% 


53.0% 


33.6% 


54.2% 


1.06 













The amount available is too small to make it of any impor- 
tance in the paving industry, and this and the preceding pyro- 
bitumen have been merely mentioned to complete our illustra- 
tion of the various types which are found in nature. Some deter- 
minations of its characteristics resulted as follows: 



220 



THE MODERN ASPHALT PAVEMENT. 
WURTZILITE. 



Test number 


15270 


31724 


72684 


PHYSICAL PROPERTIES. 




Specific gravity, 78° F./78° F., original 
substance, dry 


1.0544 


1.0490 


1.0639 


CHEMICAL CHARACTERISTICS. 








Bitumen soluble in CS 2 , air temperature. 




12.8% 


6.7% 


Bitumen yields on ignition: 

Fixed carbon 


8.8% 


5.2% 


8.3% 





SUMMARY. 

The several solid native bitumens which are not asphalts are 
shown to have interesting characteristics and some valuable 
properties. 

Grahamite, like gilsonite, can be fluxed with asphaltic oils at 
very high temperature and in such form makes a very rubbery 
material of value in the paving industry as well as for paint and 
varnish and for waterproofing. The use of Grahamite in the 
construction of pavements is limited by the fact that it may be 
utilized only at high temperatures with certain modifications and 
that the supply is extremely small. 

The other solid bitumens are of interest only in connection 
with the manufacture of varnishes and for insulating purposes; 
they do not offer inducements towards introducing them into 
the paving industry. 



CHAPTER XII. 
ASPHALTIC SANDS AND LIMESTONES. 

Kentucky. — Sands are found in Carter and Boyd Counties in 
the northeastern part of Kentucky and in the counties of Brecken- 
ridge, Grayson, Edmonson, Warren, and Logan in the western 
part of the State. The geological relations of these sands and 
the manner of their occurrence is described in great detail by 
Eldridge. 1 

In the present place it will only be necessary to show the nature 
of the sands and that of the bitumen with which they are impreg- 
nated in order to determine their availability for paving purposes. 

In a general way it may be said that the sands are all com- 
posed of loose grains which fall to pieces on the extraction of the 
bitumen and are in no case sandstone. The bitumen impregna- 
ting the sand is not a solid one, but consists of a maltha which 
pulls out to a long thread at ordinary temperature or, in rare 
instances, after extraction has a penetration as low as 60°. The 
bitumen from the Green River sand which was extracted with 
carbon disulphide had the following characteristics: 

BITUMEN EXTRACTED FROM BITUMINOUS SAND FROM THE 
GREEN RIVER DEPOSIT, KENTUCKY. 

Penetraton at 78° F 60° 

Per cent of total bitumen soluble in 88° naphtha .... 65 . 4 
Per cent of soluble bitumen acted upon by H 2 S0 4 . . 15.0 

Bitumen contains soft paraffines 2 . 6% 

Yields on ignition: 

Fixed carbon 15 . C% 

It appears from the preceding figures that the bitumen of the 
Kentucky sands is semi-asphaltic in that it yields an amount of 

1 The Asphalt and Bituminous Rock Deposits of the United States, 1901. 

221 



222 



THE MODERN ASPHALT PAVEMENT. 



fixed carbon corresponding to that found in the asphalts, but at 
the same time contains some soft paraffine scale, and is largely 
made up of stable hydrocarbons which are not attacked by sul- 
phuric acid. As a rule, the bitumen is, however, too soft to be 
suitable for use as a paving cement until the volatile oils have 
been driven off by heating. When the bitumen is heated, how- 
ever, it is, as in the case of the California Carpinteria sands, rapidly 
converted into a hard pitch. The Kentucky sands contain on the 
average about 6.5 per cent of bitumen of the nature which has been 
described. In exceptional cases it reaches 13 per cent. The 
characteristics of the sands in particular localities are as follows : 

Carter County. — A deposit of bituminous sand occurs on Soldier 
Creek in Carter County, as described by Eldridge. Samples of 
this sand analyzed in the author's laboratory in 1898 and 1900 
had the following composition: 

BITUMINOUS SAND FROM SOLDIER CREEK, CARTER COUNTY, 

KENTUCKY. 



Test number 


10681 


33896 




1898 


1900 


Bitumen soluble in CS, 


8.2% 


9.1% 


Passing 200-mesh sieve 


4.5 


3.9 


100- " " 


21.2 


35.0 


CO-. " " 


31.0 


36.0 


50- " " 


27.6 


15.0 


" 40- " " 


3.5 


1.0 


30- " " 


2.8 


0.0 


" 20- " " 


1.2 


0.0 


100.0 


100.0 



The extracted bitumen is a soft maltha flowing slowly at 78° F., 
and hardening rapidly on heating, with a loss of 12 per cent. 

Breckenridge County. — The sandstones of Breckenridge County 
are worked by the Breckenridge Asphalt Company and lie, accord- 
ing to Eldridge, two miles south of Garfield, in a bed 14 feet thick, 
the lower 7 or 8 feet being much more enriched than the upper 
portion. Specimens examined in the author's laboratory had 
the following composition: 



ASPHALT1C SANDS AND LIMESTONES. 



223 



BITUMINOUS SAND FROM DEPOSIT OF BRECKENRIDGE AS- 
PHALT COMPANY, BRECKENRIDGE COUNTY, KENTUCKY. 

Test No. 9264. 





Richer Portion. 


Poorer Portion. 


Bitumen soluble in CS„ 


7.7% 


4.3% 


Passing 200-mesh sieve 


7.2 


10.6 


" 100- " " 


26.6 


26.6 


80- " " 


26.0 


26.0 


50- " " 


29.4 


29.4 


" 40- " " . 


2.5 


2.5 


" 30- " " 


0.4 


0.4 


" 20- " " 


0.2 


0.2 


100.0 


100.0 



The extracted bitumen is a soft maltha hardening on heating, 
as is the case with bitumens from other Kentucky sands. 

Grayson County. — Asphaltic sands are found in Grayson County 
in the neighborhood of Leitchfield, which Eldridge describes under 
the designation " Schillinger Prospects " and " Breyfogle Quarries." 
At the latter point sands impregnated with bitumen and seepages 
of a gummy consistency are found. The sands are of varying 
degrees of richness and the seepages of different degrees of hard- 
ness. The results of analyses of specimens of the materials which 
were formerly mined at this point are given in the following tables 
and in one on p. 225: 

ASPHALTIC SANDS, GRAYSON COUNTY, KENTUCKY. 



Test number 


41187 

6% 

4 

6 

3 

5 

7 
20 
29 
13 

7 


41277 

10% 
13 
63 
11 

3 












41188 

13% 

5 

6 

6 
52 
18 










49577 


Bitumen soluble in CS 2 


13.7% 
4.3 


Passing 200-mesh sieve 


11 100- " " 


4.0 


80- " " 


6.0 


" 50- " " 


34 


" 40- " " 


24.0 


30- " " 


8.0 


20- " " 


3.0 


10- " " 


3.0 


Retained on 10-mesh sieve 






100 


100 


100 


100.0 



224 



THE MODERN ASPHALT PAVEMENT. 



BITUMEN IMPREGNATING MINERAL MATTER, GRAYSON 
COUNTY, KENTUCKY. 



Test number 

Specific gravity, 78° F./78° F 

Color 

Lustre 

Structure 

Fracture 

Hardness 

Odor 

Loss, 220° F., 1 hour 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble 88° naphtha, air tempera 

ture 

This is per cent of total bitumen 

Bitumen soluble 62° naphtha, air tempera 

ture 

This is per cent of total bitumen 

Bitumen yields on ignition : 

Fixed carbon 

Penetration of extracted bitumen at 78° F. 



41189 

1.282 

Black 

Shining 

Massive 

Irregular 

-1 
Asphaltic 

7.0% 

62.4% 

9.2 
28.4 



100.0 



50.8% 
83.0 



54.3% 
87.0 



12.0% 
45° 



41190 

1.769 

Black 

Shining 

Massive 

Irregular 

1 
Asphaltic 

1.5% 

30.0% 

4.9 
65.1 



100.0 



21.9% 
70.3 



29.7% 
79.0 



12.0% 
35° 



It will be noticed that in the case of the sand some of it is 
quite rich in bitumen and other parts of it quite poor. The sand 
grains are extremely coarse, the majority of them being of 50- 
and 40-mesh size in one instance, and larger than 30 in another. 
Such a sand grading alone would make this material unsuitable 
for use in an asphalt surface. 

The mixture of loose mineral matter and asphalt contains a 
large percentage of bitumen which is very hard in consistency 
but is hardly asphaltic in nature, as the amount of fixed carbon 
which it yields is only 12 per cent. 

The seepages vary in consistency from that of a mere maltha 
to that of a bitumen having a penetration of only 35°. In the 



ASPHALTIC SANDS AND LIMESTONES. 



225 



SEEPAGES, GRAYSON COUNTY, KENTUCKY. 



Test number 

Specific gravity 78° F./78° F. 
3, 220° F., 1 hour 



Dry substance: 

Loss, 325° F., 7 hours 

" ,400°F.," " (fresh sample). 
Character of residue after 325° F. . . 



400° F. 



Bitumen soluble in CS 2 , air temperature. 

Difference 

Inorganic or mineral matter 



Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen 

Bitumen soluble in 62° naphtha, air tem- 
perature 

This is per cent of total bitumen 



Bitumen yields on ignition: 
Fixed carbon 



Penetration of extracted bitumen at 78° F. . 



41192 



26.8% 



4.1% 
12.4 
Too soft for 
penetration. 

22° 

89.8% 
0.3 
9.9 



100.0 



74.5% 
83.0 

81.0% 
90.2 



41277 

.9783 
19.2% 



88.6% 
5.5 
5.9 



100.0 



54.0% 
61.2 

60.8% 
68.7 



15.6% 
35° 



latter case the material seems to be more asphaltic, as it yields 
15.6 per cent of fixed carbon. 

A deposit identified to the author ac being from Ferry's quarry, 
in Grayson County, has the following characteristics: 

BITUMINOUS SAND FROM FERRY'S QUARRY, GRAYSON 

COUNTY, KENTUCKY. 

Test No. 7218. 

Bitumen soluble in CS 2 7 . 7% 

Passing 200-mesh sieve 17.7 

" 100- " " 34.5 

" 80- " " 36.4 

" 50- " " 3.7 



100.0 

EXTRACTED BITUMEN. 

Bitumen soluble in 88° naphtha, air temperature 71 .4% 

Loss, 400° F., 7 hours 18.6 

Penetration at 78° F 81° 



226 



THE MODERN ASPHALT PAVEMENT. 



This material is composed of an extremely fine sand, quite 
different from that found at the Breyfogle quarry, and contains 
between 7 and 8 per cent of bitumen, which, after heating for 7 
hours at 400° F., loses 18.6 per cent. This bitumen, before heat- 
ing, has a penetration of 81°. 

Edmonson County. — Eldridge states that in Edmonson County 
there are many deposits of asphaltic sandstone and small tar 
springs, none of which he considers to be of any value. They have 
not been examined in the author's laboratory. 

Warren County. — Along the Green River, in Warren County, 
are deposits of bituminous sand which have been worked for 
paving purposes, the characteristics of which are that they con- 
sist of quartz sand impregnated with from 6 to 9 per cent of very 
soft maltha. 

At Youngs Ferry the Green River Asphalt Company has opened 
a quarry the sand from which has the following compositions: 



BITUMINOUS SAND FROM DEPOSIT OF GREEN RIVER ASPHALT 
COMPANY, WARREN COUNTY, KENTUCKY. 



Test number 


61873 

6.1% 


27606 

8.8% 


Bitumen soluble in CS 2 


Passing 200-mesh sieve 


14.9 


11.3 


100- " " 


48.0 


10.0 


80- " " 


19.0 


23.0 


50- " " 


12.0 


37.1 


40- " " 


0.0 


8.0 


30- " " 


0.0 


.9 


" 20- " " 


0.0 


.9 


10- " " 


0.0 


.0 


100.0 


100.0 


Loss, 212° F. , 1 hour 




1.5% 





EXTRACTED BITUMEN. 

Penetration at 78° F Too soft, pulls to a thread 

Fixed carbon 11.8% 

The first column represents the average composition of that 
which has been taken out for paving purposes. It is very evi- 
dent that the small percentage of bitumen in this sand, aside 



ASPHALTIC SANDS AND LIMESTONES. 



227 



from the fact that it is not of a strictly asphaltic nature, as it 
yields but 11.8 per cent of fixed carbon, would make it impossible 
to produce a satisfactory surface mixture with it without some 
amendment. 

Near Brownsville the Rock Creek Natural Asphalt Company 
has worked another sand which is coarser than that found at 
Youngs Ferry, as shown by the following analysis: 

BITUMINOUS SANDSTONE NEAR BROWNSVILLE, KENTUCKY. 
Test No. 61363. 

Bitumen soluble in CS 2 6.6% 

Passing 200-mesh sieve 12 .4 



100- 
80- 
50- 
40- 
30- 
20- 
10- 



7.0 

3.0 

18.0 

30.0 

13.0 

6.0 

4.0 

100.0 



This material, like that from the Youngs Ferry deposit, is 
not sufficiently rich in bitumen to make it of any value. 

Oozings of this bitumen, collected in drill-holes, had the com- 
position given in table on page 228 under test No. 40894. 

The bitumen in the sands at this point is a very soft one, 
having a penetration of 193°. It hardens rapidly on heating, 
the residue after 7 hours at 400° F. having a penetration of only 
12°. Such an unstable bitumen, aside from the unsatisfactory 
grading of the sand, makes this sand unavailable for the produc- 
tion of a satisfactory pavement. 

Logan County. — Eldridge states: "The deposits of bituminous 
sandstone in Logan County lie in its northern half. ... A single 
quarry of the Standard Asphalt Company has been opened about 
5 miles northeast of Russellville." 

The average material from the base of the quarry has the com- 
position given in table on page 228, test No. 19938. 

The bitumen which oozes from the sand has been examined 
with the results given in table on page 229. 



228 THE MODERN ASPHALT PAVEMENT. 

OOZINGS OF BITUMEN FROM NEAR BROWNSVILLE, KENTUCKY. 

Test No. 40894. 
Loss, 212° F., until dry 22.8% 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 11.5% 

Residue after heating to 325° F Penetration = 55° 

Loss, 400° F. for 7 hours (fresh sample) 13 . 1% 

Residue after heating to 400° F Penetration = 12° 

Bitumen soluble in CS 2 , air temperature. .... 94.4% 

Difference .5 

Inorganic or mineral matter 5.1 



100.0 



Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 75 . 6% 

This is per cent of total bitumen 80 . 

Bitumen soluble in 62° naphtha, air tem- 
perature 82.6% 

This is per cent of total bitumen 88 . 

EXTRACTED BITUMEN. 

Penetration a 78° F = 193° 

BITUMINOUS SANDSTONE, LOGAN COUNTY, KENTUCKY. 
Test No. 19938. 

Bitumen soluble in CS 2 7 . 8% 

Passing 200-mesh sieve 6.2 

100- 



80- 
50- 
40- 
30- 



Loss at 212° F. 



27.0 


31.0 


25.0 


2.0 


1.0 


100.0 


• 5% 



These results show that this material, like the bitumen in 
the sands from other parts of Kentucky, is a maltha which 
hardens on heating to a very brittle substance, and on that account 
is not suitable for paving purposes. 



ASPHALTIC SANDS AND LIMESTONES. 229 

BITUMEN OOZING FROM SAND, LOGAN COUNTY, KENTUCKY. 
Test No. 21264. 

Loss, 212° F., until dry 16.3% 

Dry substance : 

Loss, 325° F., 7 hours 5.5% 

Residue after heating to 325° F Too soft for 

penetration 

Loss, 400° F., 7 hours 3.8% 

Residue after heating to 400° F Penetra- 
tion =20° 
Bitumen soluble in CS 2 , air temperature. . . 62.8% 

Difference 7.7 

Inorganic or mineral matter 29 . 5 

100.0 
Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 35 . 4% 

This is per cent of total bitumen 56 . 4 

Bitumen soluble in 62° naphtha, air tem- 
perature 50 . 6% 

This is per cent of total bitumen 80 . 6 

Importance of the Kentucky Bituminous Sands for the Paving 
Industry. — From the preceding data it is very evident that no 
satisfactory asphalt pavements can be constructed from any of 
the bituminous sands available in Kentucky for two reasons. 
In the first place the bitumen is a maltha which has no stability 
and hardens very much on exposure to high temperatures. In 
the second place it is not present in sufficient amount to cement 
the sand grains together satisfactorily, and finally, the sand itself 
is seldom graded in a way to form a satisfactory mineral aggregate. 
It is always deficient in filler. It may be possible, for light traffic 
streets, to make an asphalt surface mixture from a Kentucky 
sand by the addition of some hard bitumen and a satisfactory 
amount of filler, but when this is done it would generally be found 
to have been a matter of economy not to have used the bituminous 
sand at all, but to have started with a suitable local sand and have 
combined this with a proper asphalt cement and a good filler. 

Actual experience with asphalt pavements constructed with 



230 THE MODERN ASPHALT PAVEMENT. 

Kentucky material has confirmed all these conclusions, and it is 
safe to say that the sooner the attempt to work these deposits is 
abandoned the less money will be sunk. 

Oklahoma. — Deposits of bitumen in various forms are found 
widely scattered over this State. Among them are several 
which consist of bituminous sands. Although none of them 
is of any great value in the paving industry, it will be of interest 
here to show what their composition is in order that vain 
attempts may not be made to utilize them at great financial 
loss. 

Limestones saturated with bitumen are also found in the 
immediate neighborhood of the bituminous sands, and as attempts 
have been made to utilize these in conjunction with the sands 
they will be described at the same time. 

In what Eldridge denominates the Buckhorn District, in the 
region east of the Washita River and in the neighborhood of Rock 
Creek, numerous quarries of bituminous sands and limestones have 
been opened by different individuals and companies and some of the 
material has been utilized in the construction of street pavements. 

The material from the Ralston quarry, about 2 miles west- 
northwest of Schley and 8 miles northeast of Dougherty, has the 
following composition. This material is still further described 
by Eldridge. 1 

FROM RALSTON QUARRY, NEAR SCHLEY AND DOUGHERTY, 

OKLAHOMA. 

Test No. 11602. 

Bitumen soluble in CS 2 5 . 0% 

Passing 200-mesh sieve 9.7 

100- " " 41.0 

80- " " :... 29.0 

50- " " 11.0 

" 40- " " 2.0 

" 30- " " 1.0 

" 20- " " 1.0 

" 10- " " 3 

100.0 



The Asphalt and Bitumimous Deposits of the U. S., 1901, 294. 



ASPHALT1C SANDS AND LIMESTONES. 



231 



EXTRACTED BITUMEN. 

Extracted bitumen : a soft maltha, consistency of residuum. 

Loss, 325° F. , 7 hours 5.96% 

" 400° F., 5 " (fresh sample) . 9.98% 

Residue after heating to 400° F Pulls to a long 

thin thread 
and pene- 
trates 76°. 

The Gilsonite Roofing and Paving Company's mines of bitu- 
minous limestone and asphaltic sands are found in Sections 21, 
22, and 23, Range R.3.E. The Rock Creek Natural Asphalt 
Company own and have somewhat developed several deposits 
of bituminous sands and limestone rocks north of the preceding 
deposits, in the Buckhorn District. 

The sands which have been developed to the greatest extent 
and used by the Rock Creek Natural Asphalt Company have the 
following composition: 

BITUMINOUS SAND FROM BUCKHORN DISTRICT, OKLAHOMA. 



Test number 


30481 

12.2% 

1.8 
29.0 
26.0 
30.0 

1.0 


69086 

11.1% 
12.9 
48.0 
23.0 

5.0 

0.0 


Bitumen soluble in CS 2 


Passing 2C0-mesh sieve 


ion- " " 


80- " " 


50- " " . 


40- " " 


Extracted bitumen at 78° F. . . . .... 


100.0 


100.0 
Soft 



This sand is fine and somewhat variable in grading, the bitu- 
men which it contains is a soft maltha, although it varies some- 
what in accordance with the extent to which it has been weathered. 
The material has been combined with the limestones, a description 
of which follows, and fairly successful pavements have resulted 
from the combination in Kansas City, Mo. 

The principal bituminous limestone quarries of the Gilsonite 
Roofing and Paving Company are known as No. 2 and No. 4, the 
former being found at the southeast end of the so-called Buck- 



232 



THE MODERN ASPHALT PAVEMENT. 



horn District, while the No. 4 quarry or mine is at the western end 
of the District about 1 mile west of Schley and 7 miles northeast 
of Dougherty. The composition of these limestones is as follows: 

BITUMINOUS LIMESTONE FROM BUCKHORN DISTRICT, 
OKLAHOMA. 

Test No. 69084. 
lime rock no. 4. 

Bitumen soluble in CS 2 4.3% 

Carbonates and organic matter 86 . 8 

Mineral matter insoluble in HC1 8.9 



Extracted bitumen penetrates at 78° F. . 

LIME ROCK NO. 2. 



100.0 
60° 



Test number 


69085 

12.1% 

76.5 

11.4 


57870 

13.1% 
81.6 
5.3 


Bitumen soluble in CS 2 


Carbonates and organic matter 


Mineral matter insoluble in HC1 

Extracted bitumen penetrates at 78° F. . . 


100.0 
65° 


100.0 
21° 



In thin section under the microscope it is seen that these lime- 
stones differ entirely in their structure from those found on the 
Continent of Europe and which have been utilized so largely for 
the construction of pavements. The mineral matter in the latter 
consists entirely of the remains of marine animal life that are very 
uniformly impregnated with bitumen. The limestones from 
Oklahoma on the other hand, contain a very consider- 
able proportion of hard crystalline calcite which is not impreg- 
nated at all with bitumen. On this account the latter do not 
compare favorably with the rock asphalts of Europe. 1 

These limestones, as has been said previously, have been com- 
bined with the sand rock to make a very satisfactory paving sur- 
face, the proportions in use being J No. 2 lime rock, J No. 4 lime 
rock, and ^ sand rock. The sand rock supplies the flux necessary 
for the hard bitumen in the limestone, the latter having a pene- 

1 See page 252. 



ASPHALTIC SANDS AND LIMESTONES. 233 

tration of only 60 to 65°, before heating, as it occurs in nature 
and only 20° after that operation. Such a mixture has the follow- 
ing composition: 

SURFACE MIXTURE MADE FROM BITUMINOUS SAND AND LIMB 

ROCKS FROM OKLAHOMA. 

Test No. 48231. 

Bitumen soluble in CS 2 8.2% 

200-mesh sieve 18.8 



" 100- " " 


9.0 


" 80- " " 


18.0 


" 50- " " 


16.0 


" 40- " " 


4.0 


" 30- " " 


3.0 


" 20- " " 


8.0 


" 10- " " 


6.0 


Retained on 10-mesh sieve 


9.0 



100.0 
It will be noticed that the bitumen in this mixture is lower 
than in a sand mixture of the same grading and yet it has been 
shown by experience that it is a satisfactory one. This is prob- 
ably due to the fact that the film of asphalt on the lime rock is 
not necessarily as thick as that upon the sand grains and for this 
reason the percentage of bitumen which this mineral aggregate 
will carry is smaller than when the latter is of a silicious nature. 
Although fairly satisfactory pavements have been made with 
these materials it is not probable that they will prove of any impor- 
tance in the paving industry as the supply as turned out is too 
small to permit of obtaining a requisite quantity of uniform quality 
and because the greatest skill is necessary in so handling the mate- 
rial as to make it possible to put it down with the bitumen of a 
proper state of consistency, as this changes very readily on being 
heated in the slightest degree to too high temperature. 

Brunswick District. — The District which has been named by 
Eldridge the " Brunswick District " lies on the Brunswick Creek 
immediately north of Rock Creek, to which it is a tributary, 4 miles 
northeast of Dougherty. The deposits here resemble those found in 
the Buckhorn District. They have been worked to a certain extent 
industrially but are probably of no great commercial interest. 



234 



THE MODERN ASPHALT PAVEMENT. 



Analyses of the bituminous products obtained there, made in 
1898, resulted as follows: 

FROM BRUNSWICK DISTRICT, OKLAHOMA. 

Test No. 18656 and 18657. Fossiliferous limestone, impregnated with bitumen r 
" " 18662. Bituminous sand, Kirby mine. 
" " 18667. " " as shipped. 

" " 18668. " " " 



Test number 


18656 

1.6% 


18657 

3.1% 

3.9 

1.0 

1.0 
11.0 
12.0 
30.0 
31.0 

7.0 


18662 

11.3% 

1.7 
29.0 
45.0 
13.0 

0.0 

0.0 

0.0 

0.0 


18667 

9.3% 

1.7 
36.0 
40.0 
13.0 

0.0 

0.0 

0.0 

0.0 


18668 


Bitumen soluble in CS 2 


8-6% 
1.4 


Passing 200-mesh sieve 


" 100- ' 


1 1 




20 


" 80- ' 


1 1 




42 


50- ' 


it 




28.0 


" 40- ' 


(C 




0.0 


" 30- ' 


11 




0.0 


" 20- ' 


( c 




0.0 


" 10- ' 


(I 




0.0 












100.0 


100.0 


100.0 


100.0 



Materials received from the same locality in 1903 had the 
following composition: 



Test number 


63279 

4-9% 
89.1 
6.0 


63280 

6.8% 
86.4 
6.8 


63283 


Bitumen soluble in CS 2 


2.3% 
94.1 


Carbonates 


Mineral matter insoluble i 


aHCl 


3.6 




100.0 


100.0 


100.0 



Remarks: No. 63279. Hard compact limestone with free bitumen in small 
seams, somewhat crystalline. 
" 63280. Same as No. 63279, containing more seams and larger 
ones and the latter being filled with a considerable 
seepage of free bitumen, aside from that impregnat- 
the rock. 
" 63283. Same as No. 63279, unevenly impregnated with bitu- 
men, the seams carrying free material, although to 
no such extent as No. 63280. 

It would seem from the above data that there can be no 
question that the lime rock will not bear the cost of transportation. 

Arbuckle Mountains. — Many deposits of bituminous sands are 
found in the neighborhood of the Arbuckle Mountains, some cf 



ASPHALTIC SANDS AND LIMESTONES. 23$ 

which have been examined by the author. That occurring south- 
east of Woodford, close to the Henry house Creek, and known as 
the Sneider Deposit, has the following composition: 

BITUMINOUS SAND FROM SNEIDER DEPOSIT, ARBUCKLE 

MOUNTAINS DISTRICT, OKLAHOMA. 

Test No. 30478. 

Bitumen soluble in CS 2 11-1% 

Passing 200-mesh sieve 8.9 

100- " " 75.0 

80- " " 2.0 

50- " " 2.0 

40- " " 1.0 

30- " " 0.0 

20- " " . 0.0 

10- " " 0.0 



100.0 
The quarry is described in detail by Eldridge. 1 
Attempts have been made to extract the bitumen from this sand, 
industrially and the material obtained has the following properties: 

EXTRACTED BITUMEN FROM BITUMINOUS SANDS FROM 

ARBUCKLE MOUNTAINS DISTRICT, OKLAHOMA. 

Test No. 30474. 

Loss, 212° F., 1 hour 0.1% 

Residue after heating to 212° F Too soft for pene- 
tration 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 3.5% 

Residue after heating to 325° F Penetration = 110° 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 



68.7% 

1.5 
29.8 


100.0 


57.3% 
83.4 


62.6% 
91.1 



Malthenes : 

Bitumen soluble in 88° naphtha, air temp. . . 

This is per cent of total bituman 

Bitumen soluble in 62° naphtha, air temp. . . 

This is per cent of total bitumen 

Character of extracted bitumen Soft at 78° F. 

The character of this material and the cost of obtaining it 
will probably exclude it from any commercial application. 
1 Asphalt and Bituminous Rock Deposits, 1901, 316. 



236 



THE MODERN ASPHALT PAVEMENT. 



The Elk Asphalt Company has a similar sand of the following 
composition : 

BITUMINOUS SAND FROM ELK ASPHALT COMPANY DEPOSIT, 

OKLAHOMA. 
Test No. 30483. 

Bitumen soluble in CS 2 8 . 7% 

Passing 200-mesh sieve 10 . 3 



100- 
80- 
50- 
40- 
30- 
20- 
10- 
Retained on 10-mesh sieve. 



7.0 

10.0 

34.0 

12.0 

4.0 

4.0 

6.0 

4.0 



100.0 
Character of extracted bitumen = Soft maltha. 

From this sand a bitumen has been extracted having the follow- 
ing composition: 

BITUMEN EXTRACTED FROM ELK ASPHALT COMPANY'S 

DEPOSIT OF BITUMINOUS SAND, OKLAHOMA. 

Test No. 30475. 

Loss, 212° F., 1 hour 0.2% 

Consistency of residue after heating Too soft for 

penetration 

DRY SUBSTANCE. 

Loss, 325° F., 7 hours 4.2% 

Consistency of residue after heating Too soft for 

penetration 

Bitumen soluble in CS 2 , air temperature 88 . 0% 

Difference ., 3.1 

. Inorganic or mineral matter 8.9 



100.0 



Malthenes : 

Bitumen soluble in 88° naphtha, air temperature. . . 79 . 1% 

This is per cent of total bitumen 89 . 9 

Bitumen soluble in 62° naphtha, air temperature . . 85.4% 

This is per cent of total bitumen 96 . 6 

Extracted bitumen Too soft for 

penetration 



ASPHALTIC SANDS AND LIMESTONES. 



237 



Upon this material the same remarks may be made as in the 
sase of the Sneider bitumen. 

Near Emet, in the same neighborhood, bituminous sands are 
found which have the following characteristics: 

DEPOSIT OF BITUMINOUS SAND NEAR EMET, OKLAHOMA 
Test No. 30477. 

Bitumen soluble in CS 2 10 .4% 

Passing 200-mesh sieve 2.6 



tt 


100- 


( t t 


tt 


80- 


tt t 


H 


50- 


tt t 


It 


40- 


tt t 


It 


30- 


tt t 


tt 


20- 


tt t 


tt 


10- 


tt i 



2.0 


5.0 


63.0 


16.0 


1.0 


0.0 


0.0 


100.0 


Soft maltha 



Consistency of extracted bitumen = . . . 

This sand, like the others, is impregnated with a soft maltha. 

In the Quapaw Reservation a sand occurs which contains 
from 16 to 18 per cent of bitumen, the sand grains having the 
following grading : 

BITUMINOUS SAND, QUAPAW RESERVATION, OKLAHOMA. 



Test number. . „ 


30479 

18.0% 


30141 

- 16.5% 


Bitumen soluble in CS 2 


Passing 200-mesh sieve 


29.0 


37.3 


100- " '•' 


12.0 


10.1 


" 80- " " 


4.0 


5.0 


" 50- " " 


12.0 


19.0 


" 40- " " 


7.0 


10.0 


30- " " 


3.0 


.7' 


20- " " 


2.0 


.7 


10- " " 


4.0 


.7 


Retained on 10-mesh sieve. . 


9.0 


.0 


100.0 


100.0 



This sand apparently contains some organic matter not of a 
bituminous nature. 

Bituminous Limestone at Ravia. — Just south of the Washita 
River and Tishomingo, at Ravia, is a large deposit of bituminous 
limestone. This contains 7.1 per cent of bitumen with varia- 



238 



THE MODERN ASPHALT PAVEMENT. 



tions between 2.3 and 13.2 per cent. The bitumen is a rather 
dense maltha having a penetration of 210° on extraction. The 
limestone does not break down on extraction with solvents and 
in thin section under the microscope is shown to be of uneven 
texture containing crystals of calcite which are not impregnated 
with bitumen. The rock is not made up, as in the case of the 
Continental asphaltic limestones, of the remains of marine organ- 
isms. Owing to this fact and the small percentage of bitumen 
in the rock it can be of no commercial interest. Several samples 
from the face of the mine give the following results on analyses: 



BITUMINOUS LIMESTONE FROM RAVIA, OKLAHOMA. 



Test number. 



Bitumen by CS 2 

Mineral matter insoluble 

inHCl 

Mineral matter soluble in 

HC1 

Difference 



67316 


67317 


67318 


67319 


67320 


10.8% 


7.3% 


7.0% 


3.4% 


9.9% 


18.5 


15.5 


14.3 


30.8 


11.3 


69.9 

.8 

100.0 


75.8 
1.4 


73.2 
5.5 


63.7 
2.1 


77.9 
.9 


100.0 


100.0 


100.0 


100.0 



67321 

9.6% 

17.9 

71.3 
1.2 

100.0 



The Ravia rock is typical of all American asphaltic limestones 
and for this reason it is hardly to be believed that any of them 
possess the same desirable features as those which are mined in 
Europe. 

Other deposits in the Arbuckle Mountain region are of much 
the same character as those which have been described and are 
of no commercial interest. 

Eldridge states that at Wheeler there is one of the largest 
oil seepages in the United States. The character of the maltha 
at this point is very much the same as that which has been extracted 
from the sandstone. It is, of course, impossible to collect it in 
sufficient quantity to be employed in the paving industry. 

Five miles northwest of Ardmore a stratum of bituminous sand- 
stone is found having a dip which is nearly vertical. Many attempts 
have been made to utilize this material by boiling it with water f 
but they have all been failures and have resulted in the loss of 
considerable capital in the same way that has been the case else- 



ASPHALTIC SANDS AND LIMESTONES. 



239 



where in Oklahoma. The best of the rock available at this point 
has the following composition: 

BITUMINOUS SANDSTONE NEAR ARDMORE, OKLAHOMA. 



Test number 


47443 

9.6% 
12.4 
50.0 
25.0 

2.0 

1.0 

0.0 

0.0 

0.0 

100.0 


47444 

11.8% 

1.2 

5.0 
16.0 
59.0 

6.0 

1.0 

0.0 

0.0 


Bitumen soluble in CS 2 

Passing 200-mesh sieve 

11 100- " " 

80- " " 

" 50- " " 

" 40- " " 

" 30- " " 

" 20- " 


10- " " 


ioo.o ; 



Penetration of extracted bitumen at 78° F. =44°. Too soft for pen. 

In the preparation of the bitumen by extraction it is impossible 
to remove all the fine material and the maltha is much hardened 
in the process of boiling out the water. A sample of the so-called 
refined material contained 77.8 per cent of bitumen which had a 
penetration of 75°. 

Grahamite in Oklahoma. — There are several occurrences 
of grahamite in Oklahoma, the chief one being in what Eldridge 
has denominated the Tenmile Creek District. This has been 
described in detail under the heading "Grahamite." 1 At 
another point, near Loco, in Section 36, T.2.S., R.4.W., gra- 
hamite has been found in a network of veins which is remarkable 
as containing from 23.6 per cent to 2.4 per cent of pyrites, evi- 
dently introduced by infiltration. No commercial supply of 
this material is available. 

Eldridge has classified these materials as " Asphaltites " and 
regards that found at the so-called Moulton mine as closely resem- 
bling albertite. He has named it Impsonite. The author sees 
no reason to use the word Asphaltite as applied to these bitu- 
mens as its original use was quite different. It is a fact that the 
weathered bitumen at the Moulton deposit on the surface lesembles 
albertite to a considerable extent, being only slightly soluble in 



See page 211. 



240 THE MODERN ASPHALT PAVEMENT. 

the ordinary solvents for bitumen. As the material has been 
taken out deeper down in the vein it is found to be entirely soluble 
in carbon disulphide, to yield a percentage of fixed carbon which 
is characteristic of grahamite and in every way to resemble closely 
the type grahamite originally described from Ritchie County, 
West Virginia. It cannot, therefore, be properly assigned a new 
name, Impsonite. . 

The Value of the Deposits of Oklahoma in Relation 
io the Paving Industry. — From what has been said in our de- 
scription of the Oklahoma bituminous deposits it is evident 
that the only conclusion that can be drawn in regard to them 
is that they are of little industrial interest with the exception, 
perhaps, of the grahamite. The deposits, although large in amount^ 
taken as a whole are individually small and moreover, far from 
being uniform in their character, they contain too little bitumen 
and this bitumen is not sufficiently asphaltic in its character. 
It is very improbable that any return will ever be obtained for 
the amount of money that has been spent in attempting to develop 
them. 

Texas. — Bitumen is found in Texas impregnating limestone in 
Burnet and Uvalde Counties and mixed with sand in Montague 
County. 

The latter deposits are near St. Jo. They are of no commercial 
interest and resemble in many respects those found in 
Oklahoma. 

In Burnet County, Eldridge states, the deposit consists of 
Cretaceous limestones at Post Mountain, near the town of Bur- 
net, which are impregnated with from 4 to 8 per cent of bitumen, 
mostly with the latter amount. The bitumen is soft and sticky, 
penetrating 240° on extraction. The quantity of asphalt bearing 
rock is stated to be limited. 

In Uvalde County the bituminous material is found 18 to 25 
miles west of Uvalde in the region of the Anacacho Mountains. 
The only deposit which has been worked to any considerable 
extent is a peculiar limestone which Eldridge described as being 
" an assemblage of minute organisms together with a conspicuous 
proportion of crystalline calcite. Molluscan remains, often of 



ASPHALTIC SANDS AND LIMESTONES. 241 

large size, are also present. Through the mass of rock there is 
a high per cent of interstitial spaces, which in some instances 
may even exceed the solid portions. In addition to the inter- 
stitial spaces, properly so-called, are cavities produced by the 
removal of the mollusc an remains. . . ." The bitumen partially 
fills these cavities and also impregnates the limestone to a certain 
extent but the voids are never completely filled. On account of 
the nature of the rock and its great lack of homogeneity the mate- 
rial is not satisfactory for paving purposes, as is generally the 
case when calcite is present. The rock carries about 12 to 15 per 
cent of a peculiar bitumen, attempts to extract which were made 
at one time. Although it is now of no commercial value the 
character of the bitumen may be noted with interest. 

Asphaltic Rock from Litho-Carbon Company. — An average sample 
of the rock, Test No. 7293, as worked, contained 12.8 per cent of 
bitumen, the mineral matter consisting of 87.0 per cent of lime- 
stone and 1.2 per cent of silicates insoluble in the acid. The bitu- 
men extracted from this had the following characteristics: 

ASPHALTIC ROCK FROM LITHO-CARBON COMPANY. 

Softens 160° F. 

Flows 170° F. 

Per cent of bitumen soluble in 88° naphtha. . . 54 . 5 
Fixed carbon 18 .0 

ULTIMATE COMPOSITION. 

Carbon 80 .3% 

Hydrogen 10 . 1 

Sulphur 9.8 

The character of this bitumen is quite different from that in 
asphalt found elsewhere owing to the fact that, notwithstanding 
its consistency, it has a high percentage of fixed carbon and 
contains a larger amount of sulphur than is found in any asphalt 
of the same consistency. On account of these peculiar proper- 
ties it was known, at the time that an attempt was made to put 
it on the market, as Litho Carbon or Gum Asphalt. There is, 
of course, no reason to call it a gum, except from the fact that 
it might be employed as a substitute for some of the resins known 
as gums in the varnish trade. No native bitumen can possibly 
be regarded as a gum. 



242 



THE MODERN ASPHALT PAVEMENT. 



A fine grained bituminous limestone is also found on the Smythe 
Ranch, " about 20 miles a little south of west from Uvalde and 
4 or 5 miles south of the quarry of the Uvalde Asphalt Company.'! 
It is quite different in character from that which has previously 
been described. A specimen of the material examined in the 
author's laboratory had the following characteristics: 

BITUMINOUS LIMESTONE FROM SMYTHE RANCHE, TEXAS. 
Test No. 22070. 

Bitumen soluble in CS 2 12 .2% 

Limestone 87 . 8 

Sand insoluble in HC1 1.2 



100.0 



EXTRACTED BITUMEN. 

Consistency Hard-friable 

Softens: 240° F. 

Flows 250° F. 

Fixed carbon 16 .9% 

Bituminous sandstones are also found in Uvalde County and 
consist of an extremely fine sand, the larger portion passing the 
100-mesh sieve, impregnated with a bitumen yielding a large 
amount of fixed carbon and, therefore, similar to that found in 
the limestone. 

BITUMINOUS SANDSTONE, UVALDE COUNTY, TEXAS. ' 



Test number. 


22071 

9.8% 
90.2 


22072 

8.1% 
91.9 

100.0 
93.6% 
91.9% 


Bitumen soluble in CS 2 

Sand 


Per cent of the sand insoluble 
in HC1 


100.0 
96.5% 

88.2% 


Per cent of the sand passing- 
100-mesh sieve 





EXTRACTED BITUMEN. 

Softens 210° F. 

Flows 220° F. 

Fixed carbon 19.5% 



ASPHALTIC SANDS AND LIMESTONES. 



243 



Bituminous Sands of California. — The location of the bitu- 
minous sands of California has been described in detail by Eld- 
ridge. It will suffice to remark here upon the character of some 
of the most important. 

Santa Cruz Bituminous Sands. — The quarries of bituminous 
sand near the summit of the Empire Ridge, facing the Bay of 
Monterey and the Pacific Ocean, are of very large extent. The 
individual strata are very variable in composition, as can be 
seen from the results of an examination of the various types 
found there, collected by the author in 1898: 

BITUMINOUS SANDS, SANTA CRUZ, CALIFORNIA. 

Test No. 13578. Soft material from the foot of Point Quarry. 

" " 13579. Top of stratum, Side Hill Quarry. 

" " 13580. Richest rock, Side Hill Quarry. 

" " 13581. Lowest stratum, Rattlesnake Quarry. 

" " 13582. 6 to 9-foot vein, Hole Quarry. 

" " 13583. Poorer rock, Hole Quarry. 

*' " 13584. Gray rock, Hole Quarry. 

" 13585. 6 to 9-foot vein, Last Chance Quarry. 



Test number 


13578 

14.4% 

6.4 

2.2 
10.0 
29.0 
10.0 
15.0 

9.0 

4.0 


13579 

15.4% 

5.2 

3.4 
10.0 
30.0 
10.0 
17.0 

6.0 

3.0 


13580 

13.2% 

8.6 

5.2 
12.0 
40.0 
13.0 

5.0 

2.0 

1.0 


13581 


Bitumen soluble in CS 2 


15.1% 
1.5 


Passing 200-mesh sieve 


100- " " 

" 80- " " 


7.4 
10 


50- " " 

" 40- " " 


35.0 
13 


" 30- " " 


10 


" 20- " " 


5.0 


" 10- " " 


3 








100.0 


100.0 


100.0 


100.0 



Test number. 



Bitumen soluble in CS 2 

Passing 200-mesh sieve. 

" 100- " 

80- " 

50- " 

" 40- " 

30- " 

20- " 

" 10 " 



13582 


13583 


13584 


17.3% 


11.4% 


H.7% 


5.6 


1.5 


4.7 


24.1 


4.1 


26.6 


39.0 


12.0 


33.0 


11.0 


35.0 


20.0 


3.0 


20.0 


3.0 


0.0 


11.0 


1.0 


0.0 


4.0 


0.0 


0.0 


0.0 


0.0 


100.0 


100.0 


100.0 



13585 

14.2% 

2.4 

2.4 

6.0 
39.0 
18.0 
14.0 

4.0 

0.0 



100.0 



244 



THE MODERN ASPHALT PAVEMENT. 



The bitumen which these sands contain is in the form of 
maltha, much of it readily staining the hands when the sands 
are handled. It hardens on heating with a loss ol the lighter 
oils and a reduction in the percentage of bitumen to a point which 
makes it possible to produce a surface mixture which will with- 
stand traffic. 

It will be noted that the grading of these sands is sufficiently 
fine and that they contain a certain amount of 200-mesh material. 

The streets which have been paved with the Santa Cruz bitu- 
minous sands in San Francisco have been only fairly satisfactory. 
They have required large repairs which, however, are readily made 
by reheating the material, but there is now a tendency to abandon 
this form of asphalt pavement and to construct surfaces from 
properly graded sand combined with filler and a suitable pure 
bitumen. 

San Luis Obispo Bituminous Sands. — Deposits of bituminous 
sands near San Luis Obispo, in the county of the same name, 
were formerly worked to a very considerable extent, but these 
sands were much more variable in character than those found at 
Santa Cruz. Different strata contain from 8 to 16 per cent of 
bitumen and generally below 10 per cent. The following analyses 
show the characteristics of those which were available in 1898: 



BITUMINOUS SANDS, SAN LUIS OBISPO, CALIFORNIA. 



Test number 

Bitumen soluble in CS 2 . 

Passing 200-mesh sieve. 

100- " 

80- " 

50- " 

40- " 

30- " 

20- " 

10- " 



13576 

8.8% 
11.9 

6.1 
10.2 
50.0 

8.0 

1.0 

1.0 

3.0 



100.0 



13577 



11. 
4. 



■4% 
4 
6.1 
16.1 
44.0 
9.6 
5.0 
3.0 
1.0 

100.0 



The supply of the sands, which is readily available, is now 
nearly exhausted and they are no longer a commercial factor. 



ASPHALTIC SANDS AND LIMESTONES. 



245 



Bituminous Sands in Santa Barbara County. — Large deposits 
of bituminous sands occur in Santa Barbara County in the Sisquoc 
Hills, the location and geological relations of which are described 
by Eldridge. 1 

The deposit worked by the Alcatraz Company had the following 
composition : 

SANTA BARBARA COUNTY, CALIFORNIA. 



Test number 


6484 


6485 
16.5% 


Bitumen soluble in CS 2 . . . 


• 18.5% 


Passing 200-mesh sieve. . . 


12.5 


7.5 


100- " " ... 


8.0 


7.0 


80- " " ... 


3.0 


6.0 


50- " " .,. 


39.0 


20.0 


40- " " ... 


10.0 


20.0 


30- " " .... 


8.0 


14.0 


20- " " .... 


1.0 


8.0 


10- " " .... 


0.0 


1.0 


100.0 


100.0 



This is a sand of medium grade, largely 50- and 40-mesh grains, 
but carries a very considerable amount of 200-mesh material. 
The bitumen is in the nature of a maltha and was extracted from 
the sand with naphtha, sent down to the seacoast by pipe-line 
and there recovered by distillation. On heating, the original soft 
bitumen was hardened to a proper consistency for use for paving 
purposes. The process proved to be an expensive one and the 
material when extracted was of no better quality than that obtained 
by the distillation of ordinary California petroleum. After the 
expenditure of a vast amount of money the process was abandoned. 
Some of the bitumen prepared in this manner had the following 
characteristics: 

BITUMEN EXTRACTED FROM SANTA BARBARA COUNTY, 

CALIFORNIA, BITUMINOUS SANDS. 

Test No. 35202. 

Penetration at 78° F 48° 

Bitumen soluble in CS 2 , air temperature 89.4% 

Difference .3 

Inorganic or mineral matter 10 . 3 

100.0 
1 The Asphalt and Bituminous Rock Deposits, 1901, 429. 



2,43 



THE MODERN ASPHALT PAVEMENT. 



Carpinteria Sands. — One of the first bituminous sands to be 
worked in California for the purpose of obtaining a pure bitumen 
was that known as the Las Conchas deposit, occurring near the 
beach at Carpinteria, Santa Barbara County. The sand at this 
point was worked from the surface. It had the following com- 
position : 

LAS CONCHAS DEPOSIT AT CARPINTERIA, SANTA BARBARA, 

CALIFORNIA. 
Test No. 6475. 



Bitumen soluble in CS 2 


18.9% 


18.4% 


Passing 200-mesh sieve 


1.1 


4.5 


100- " " 


3.0 


3.0 


80- " " 


28.0 


25.0 


50- " " 


45.2 


48.0 


40- " " 


3.0 


1.1 


30- " " 


.8 


.0 


100.0 


100.0 


Per cent of total bitumen 






soluble in 88° naphtha .... 


83.0% 





Attempts were made, which were never very successful prac- 
tically or commercially, to extract the bitumen by boiling the 
sand with water. The material is of interest to-day only his- 
torically and as being typical of a certain class of soft bitumens 
the nature of which has been already referred to on page 128. 
They harden so on heating that a soft maltha will become con- 
verted into a brittle pitch most readily and on this account were 
the cause of the failures in the early attempts to lay asphalt sur- 
faces with California material. 

The deposits of solid bitumens in California have been con- 
sidered under the heading " Asphalt." 

Colorado. — The bitumens of Colorado consist only of a paraffine 
petroleum, in the Florence oil field, of some veins of gilsonite 
in the western portion, and of a grahamite found in Middle Park, 
the location and manner of occurrence of the latter being accu- 
rately described by Eldridge. He speaks of it as an asphalt closely 
resembling gilsonite which is, of course, quite an erroneous descrip- 
tion as it does not melt and yields 47 per cent of fixed carbon. 
It has already been described under grahamite. 1 

1 See page 214. 



ASPHALTIC SANDS AND LIMESTONES. 



247 



The paraffine petroleum furnishes a flux which, when carefully 
prepared, is entirely satisfactory for use in the asphalt paving 
industry. 

As far as the author is aware no asphaltic sands or limestones 
occur in Colorado which are of commercial importance. 

The Gilsonites and Other Solid Native Bitumens of Utah. — 
Utah has deposits of bitumen of very varied character. Gil- 
sonite veins are characteristic of this state and the material which 
they furnish has already been described. Wurtzilite and Ozo- 
cerite are found in small amounts but are of no importance to 
the paving industry, nor is the albertite which is found about eight 
miles from Helper Station on the Rio Grande & Western R.R., 
which Eldridge has unfortunately described under the new specific 
name of Nigrite, which is quite unnecessary and illustrates the dupli- 
cation of names which is common among investigators who are not 
widely acquainted with the materials which they examine. It is 
plainly an albertite as can be seen from the following determinations 
in comparison with some for the type albertite found in Nova Scotia. 

ALBERTITE. 



Test number 

Locality 

Color of powder 

Fracture 

Fusibility 

Specific gravity, 78° F./78° F 

Bitumen soluble in CS 2t air temperature 

Difference 

Inorganic or mineral matter 

Bitumen yields on ignition : 

Fixed carbon 

Sulphur 



19187 
Utah 

Black 

Irregular 

Does not 

intumesce 

1.092 

5.6% 
94.2 
.2 

37.0% 
1.06% 



7834 

Nova Scotia 

Black 

Smooth 

Intumesces 

slightly 

1.076 

5.9% 
94.1 
Trace 

29.8% 
1-2% 



Wurtzilite might be a valuable material for industrial purposes 
were it available in commercial quantities, but this is not the case. 
Ozocerite could never be of any value to the paving industry 



248 



THE MODERN ASPHALT PAVEMENT 



as it is a hard paraffine. The location of all these deposits are 
closely fixed by Eldridge. 

Bituminous Sands and Limestones. — Asphaltic limestone is 
found in the same geological horizons as those in which the alber- 
tite and wurtzilite of Utah occur and its bitumen is probably of 
the same origin. That located by Eldridge between Strawberry 
and Soldier creeks, 7 miles northwest of Clear Creek Station, 
on the Rio G. & W. R.R., is far from uniform in composition, 
which has been found in the author's laboratory to be as follows; 

ASPHALTIC LIMESTONE FROM NEAR CLEAR CREEK 
STATION, UTAH. 



Test number 

Bitumen soluble in CS 2 

Penetration of extracted bitumen at 
78° F 

Part soluble in HC1 



The ignited residue effervesces with acid. 

A limited supply of fairly pure bitumen has been obtained from 
this rock, which has the characteristics given in the table on page 249. 

This is a most remarkable bitumen since there is such a great 
variation in the solubility in 88° and 62° naphthas and since it 
yields no fixed carbon on ignition. From a scientific point of 
view it is worthy of careful study. 

Eldridge mentions deposits of asphaltic limestones in the same 
locality as that in which the wurtzilite veins occur along por- 
tions of the outer face of the Roan Plateau, on its westward exten- 
sion, across Soldier Summit. These deposits have not been iden- 
tified as any that have come into the author's hands. 

In Grand County, near the western border of Colorado, at 
the head of the West Water Canon, 20 miles north of West Water, 
free bitumen has been obtained to a certain extent, both in soft 
and hard form. This material when examined in the author's 
laboratory was found to have the characteristics given in the table 
on page 250, Test No. 60532. 




ASPHALTIC SANDS AND LIMESTONES. 249 

BITUMEN EXTRACTED FROM LIMESTONE ROCK FOUND 

NEAR CLEAR CREEK STATION, UTAH. 

Test No. 21632. 

Specific gravity, 78° F./78° F 1 .20 

Color Light brown 

Lustre Dull shining 

Structure Compact 

Fracture Conchoidal 

Hardness, original substance 1 

Fuses Readily 

Softens 210° F. 

Flows 220° F. 

Loss, 212° F., 1 hour .6% 

Bitumen soluble in CS 2 , air temperature 75 . 3% 

Difference 3.4 

Inorganic or mineral matter 21.3 

100.0 
Mineral matter soluble in HC1 48 . 4% , 

Bitumen soluble in 88° naphtha, air temperature 48 .3% 

This is per cent of total bitumen 64 . 3 

Bitumen soluble in 62° naphtha, air temperature 72 . 8% 

This is per cent of total bitumen „ 96 . 7 

Bitumen yields on ignition : 

Fixed carbon , 0.0% 

Penetration of extracted bitumen at 78° F 45° 

From the small percentage of fixed carbon which the Grand 
County bitumen yields it is evident that it is not a true asphalt, 
that it approaches in composition more nearly that of the paraffine 
series, and resembles to some degree the material described from 
the locality near Clear Creek station. 

The soft bitumen found at this point is a maltha which is very- 
pure, 98.6 per cent of bitumen, which consists almost entirely 
of ma'thenes soluble in 88° naphtha, 94.5 per cent. 

It has a specific gravity of .9874 and after heating for 7 hours 
at 325° F. hardens to a consistency of 53° and to 23° after the 
same length of time at 400° F. 

These bitumens are of no commercial, but of great scientific 
interest as they differ so markedly in their characteristics from 



250 THE MODERN ASPHALT PAVEMENT. 

other asphalts. Gilsonite may have been derived from such a 
material. 

BITUMEN FROM GRAND COUNTY, UTAH. 

Test No. 60532. 

dried crude. 

Bitumen soluble in CS 2 , air temperature 43.2% 

Difference 7.5 

Inorganic or mineral matter 49 . 3 

100.0 

EXTRACTED BITUMEN. 

Specific gravity, 78° F./78° F 1 . 037 

Color Black 

Hardness Variable 

Odor Asphaltic 

Softens 203° F. 

Flows 221° F. 

Penetration at 78° F 22° 

Loss, 212° F., 1 hour 2.8 % 

Bitumen soluble in CS 2 , air temperature 94 . 8% 

Difference 1.6 

Inorganic or mineral matter 3.6 

100.0 

Bitumen soluble in 88° naphtha, air temperature 68 . 7% 
This is per cent of total bitumen 71.0 

Bitumen soluble in 62° naphtha, air temperature 90 . 3% 
This is per cent of total bitumen 93 . 3 

Bitumen yields on ignition : 

Fixed carbon 8.0% 

Bituminous Sands. — Bituminous sandstones occur in various 
parts of Utah. The A. L. Hobson mine, 1} miles from Thistle 
Junction, is a material of the following composition: 

BITUMINOUS SAND FROM A. L. HOBSON MINE, THISTLE 

JUNCTION, UTAH. 

Test No. 21730. 

Loss, 212° F., until dry 0.1% 

Bitumen soluble in CS 2 11 . 6% 

Part soluble in HC1 20.0 



ASPHALTIC SANDS AND LIMESTONES. 



251 



It appears that this is a mixture of sand and silicates. 

About 8 miles from Sunnyside, in Carbon County, on the Rio 
G. &. W. R.R., a bituminous sand is found in large quantities 
which has the following composition: 

BITUMINOUS SAND, SUNNYSIDE, CARBON COUNTY, UTAH. 
Test No. 37048. 

Bitumen soluble in CS 2 11 .2% 

Passing 200-mesh sieve 16.8 



100- 
80- 
50- 
40- 
30- 
20- 
10- 



17.0 
18.0 
26.0 
6.0 
2.0 
2.0 
1.0 

100.0 



Mineral matter Quartz sand 

Extracted bitumen Pulls to a thread 

The mineral matter consists of quartz sand and the extracted 
bitumen possesses the characteristics of a maltha. 

In Whitmore Canon bituminous sandstone occurs nearly free 
from carbonates, the bitumen having a penetration of 35°. It 
has the following characteristics: 

BITUMINOUS SAND, WHITMORE CANON, UTAH. 
Test No. 21729. 

Bitumen soluble in CS 2 10.9% 

Passing 200-mesh sieve 17.9 



100- 
80- 
50- 
40- 
30- 



16.1 
16.1 
21.4 
14.2 
3.4 



100.0 

Per cent soluble in HC1 2.6% 

Extracted bitumen, penetration at 78° F. = 35° 

The bitumen obtained from this sand is a maltha which has 
been examined by the author with the following results: 



252 THE MODERN ASPHALT PAVEMENT. 



BITUMEN EXTRACTED FROM SAND FROM WHITMORE 
CANON, UTAH. 

Test No. 21731. 

Penetration at 78° F Too soft 

for test 

Loss, 212° F., until dry 18.6% 

Loss, 325° F., 7 hours 6.6% 

Residue after 325° F. penetrates 145° 

Bitumen soluble in CS 2 , air temperature 97 . 8% 

Difference 0.6 

Inorganic or mineral matter 1.6 

100.0 

Bitumen soluble in 88° naphtha, air temperature 89.8% 
This is per cent of total bitumen 91.8 

Bitumen soluble in 62° naphtha, air temperature 97.0% 
This is per cent of total bitumen 98 . 7 

Bitumen yields on ignition : 
Fixed carbon 5.0% 

It is evident from the small amount of fixed carbon which it 
yields that it is not asphaltic and it, therefore, corresponds in 
this respect with the bitumen found in similar Utah bituminous 
sands and limestones previously described. It would seem, there- 
fore that the bitumens of this nature found in Utah are more closely 
allied to ozocerite or to gilsonite than they are to the asphalts. 

Deposits in Other States. — Seepages of maltha and sand and 
limestone impregnated therewith are found in many other States, 
the distribution of bitumen being much more general than would 
be supposed. None of these deposits are of any commercial inter- 
est and must, therefore, be passed over. 

Continental Rock Asphalts. — The asphaltic limestones from 
the Continent of Europe, which have been the main source of 
the material for the asphalt paving industry in that country, 
are scattered through France, Switzerland, Germany, Sicily, and 
Italy. As these rocks reach the United States they have the 
composition given on pages 253 and 254. 



ASPHALTIC SANDS AND LIMESTONES. 



253 



CONTINENTAL ROCK ASPHALTS. 

Test No. 47137. Ragusa, Sicily. 

t* a 47i47_ Seyssel, France. 

" " 47153. Vorwohle. 

" " 47156. Sicula, Sicily. 

" " 47159. Neuchatel, Val de Travers. 

" " 47162. Mons. 



Test number 


47137 
9.9% 


47147 

5.9% 


47153 

7.5% 


47156 
10.2% 


47159 

9-1% 


47162 


Bitumen soluble ir 


L CS 2 . . 


8.9% 


Passing 200-mesh 


sieve . . 


37.1 


44.1 


18.5 


33.8 


36.9 


53.1 


100- " 




17.0 


10.0 


14.0 


16.0 


14.0 


9.0 


80- " 


ti 


6.0 


5.0 


21.0 


9.0 


15.0 


4.0 


50- " 


<< 


14.0 


9.0 


25.0 


18.0 


14.0 


7.0 


" 40- " 


it 


4.0 


7.0 


7.0 


8.0 


4.0 


5.0 


30- " 


n 


2.0 


7.0 


2.0 


3.0 


4.0 


3.0 


20- " 


ti 


5.0 


6.0 


3.0 


1.0 


2.0 


5.0 


" 10- " 


a 


5.0 


6.0 
100.0 


2.0 


1.0 


1.0 


5.0 




100.0 


100.0 


100.0 


100.0 


100.0 



For some of the rocks which have not been examined by the 
author reference must be made to the analyses of others. 1 See 
the table on page 254. 

These asphaltic limestones are characterized more by differences 
in the grain of the limestone than of their bitumen contents. As 
seen in thin sections it appears that the Continental asphaltic lime- 
stones consist of the remains of marine animal life, and it is 
undoubtedly this fact which gives them their uniform impregna- 
tion and their faculty of being readily compacted, as distinguished 
from American asphaltic limestones which contain very con- 
siderable proportions of hard crystalline calcite not impregnated 
with bitumen. 

The Sicilian rock may vary in bitumen from 6.6 to 11.4 per 
cent. The rock exported by the Sicula Company is about as rich — 
3000 tons examined by the author, in three samples, containing 
9.5, 9.3, and 9.9 per cent of bitumen, though some of it reaches 
12 per cent. The Mons rock is not evenly impregnated; veins 
which are pure white being scattered through the material. This 
rock is used more on account of the character of the grain than 

1 Dietrich, Die Asphaltenstrassen. 



254 



THE MODERN ASPHALT PAVEMENT. 



for its bitumen contents, which will average 6.5 per cent to 9.0 per 
cent. The rock obtained from the Seyssel mine at present is very- 
poor in bitumen, not exceeding 6 per cent and in some cases drop- 
ping to 1 per cent. It is used on account of the character of the 
grain of the stone. 



CONTINENTAL ROCK ASPHALTS. 

5. Cesi. 

6. Roccamorice. 

7. Limmer. 

8. Vorwohle. 



1. Val de Travers. 

2. Seyssel, Pyrimont. 

3. Lobsann. 

4. Ragusa. 



Bitumen 


1 

10.15% 
88.40 

0.25 


2 

8.15% 
91.30 

0.15 

olio 
6!io 

0.20 


3 

12.32% 
71.43 

5.91 
5.18 
0.31 
3.15 

1.70 


4 

8.92% 
88.21 




Sulphate of lime 




Alumina and iron oxides 

Sulphur 


0.91 


Carbonate of magnesia. , 


0.30 


0.96 
0.60 


Insoluble in acid 

Difference 


0.45 
0.45 


0.40 







Bitumen 

Carbonate of lime 

Sulphate of lime. . . ^ 

Alumina and iron oxides. 

Sulphur > 

Carbonate of magnesia. . 

Sand 

Insoluble in acid 

Difference 



7.15% 
73.76 
1.72 
3.02 



14.24 
0.10 



6 

12.46% 
77.53 
2.63 
2.17 



4.71 
0.50 



14.30% 
67.00 



17.52 



8.50% 
80.04 



4.03 
0.55 
4.77 
2.11 



The richer Sicilian rock by itself does not form a stable pave- 
ment but when some of the Seyssel or Mons rock is added to it 
stability is obtained. 

Continental rock asphalts are now used in this country almost 
solely in mastics, the extreme slipperiness of the pavement made 
with them having proved so objectionable in comparison with 
the asphaltic sand pavements that the former are no longer toler- 
ated. 



ASPHALTIC SANDS AND LIMESTONES. 255 

SUMMARY. 

The asphaltic sands and limestones of the United States have 
not been shown to be attractive to those interested in the con- 
struction of asphalt pavements. The asphaltic sands of Kentucky 
are too deficient in bitumen to make a satisfactory surface mix- 
ture and at the same time the character of the bitumen which 
they contain is altogether too oily. Successful surfaces have never 
been made with these materials unless they have been largely 
amended by the addition of a considerable amount of a harder 
bitumen and a proper proportion of filler. 

The bituminous sands of California, although they have been 
used to a very considerable extent, are now known to give results 
which cannot compare favorably in any way with the artificial 
mixtures which have been laid along parallel streets. Their use 
for heavy traffic work will no doubt be soon abandoned. 

The bituminous limestones and sands of Oklahoma 
occur in such small masses a-nd pockets that their uniformity 
can never be guaranteed. In a few instances excellent street 
surfaces have been constructed from the mixed sands and lime- 
stones obtained near Dougherty, but the character of the asphaltic 
limestones is such that they can never be used in the same way 
as the Continental asphaltic limestones, owing to the structure 
of their mineral aggregate. 

As a whole it is probable that more money has been lost in 
attempting to develop the asphaltic deposits described in this 
chapter than will ever be recovered by working them. 



CHAPTER XIII. 

RESIDUAL PITCHES, OR SOLID BITUMENS DERIVED FROM 
ASPHALTIC AND OTHER PETROLEUMS. 

If the distillation of the asphaltic petroleums of California, 
of the semi-asphaltic petroleums of Texas, or even of Russian oil 
and some paramne petroleums, is carried sufficiently far the residue 
on cooling will be found to be a solid bitumen, and from asphaltic 
oils of a more or less asphaltic nature. The properties of these 
solid bitumens and their availability for industrial purposes depend 
largely, of course on the nature of the petroleum from which 
they are derived, the care with which the distillation is conducted 
and the amount of cracking which has taken place in the process. 

Residual Pitches from California Petroleum. — The residues 
from California petroleum have been used to a very consider- 
able extent in the paving industry and are generally known as 
"D" grade asphalt or under some trade designation or brand, 
such as Diamond, Obispo, Acme, or Hercules. 

They have been, usually, all more or less carelessly manufactured 
without laboratory control and consequently vary in character and 
consistency. As a rule they are by-products resulting from the 
recovery of distillates of different gravities from crude petroleum 
and are not prepared especially for paving purposes. That 
they are badly cracked in the process of manufacture, the oil 
often being heated as high as 900° F., appears from the fact that 
if the petroleum from which they are obtained is distilled or evap- 
orated under such conditions that cracking will not occur, as 
much as 60 per cent of a hard residue will remain, as shown by 
the following figures obtained in the author's laboratory, as com- 
pared with 30 per cent by industrial methods. 

256 



RESIDUAL PITCHES. 257 

RESIDUAL PITCH FROM CALIFORNIA PETROLEUM PREPARED 
IN THE LABORATORY. 

Test No, 69209. 

Loss, 212° P., to constant weight 2.8% 

Loss, heating until 59° penetration is obtained. .. . 38.9% 

Hesidual solid bitumen penetrating 59°. 61 . 1 

100.0 

ANALYSIS OF BITUMEN PENETRATING 59°. 

Loss, 400° F., 4 hours 4.5% 

Penetration of residue after heating „ . . 29° 

Bitumen soluble in CS 2 , air temperature 99.8% 

Difference .1 

Inorganic or mineral matter. .1 

100.0 

Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 77 . 6% 
This is per cent of total bitumen 77. 8% 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air 

temperature 0.5% 

Bitumen yields on ignition: 

Fixed carbon. .... 10 . 5% 

As a matter of fact, under the conditions which obtain indus- 
trially, only 30 to 40 per cent of solid residue is recovered, the 
remainder being cracked and volatilized, and such residues con- 
tain a much larger amount of fixed carbon, 15 to 20 per cent, than 
is found on careful evaporation. With the form of still at present 
in use and with the most careful handling the temperature rises 
to 720° F. and the residual pitch is much smaller in amount, in 
the author's experience, than it should be. As an illustration 
of this, at an oil works under the author's observation, where 
an endeavor was made to produce the best " D " grade material 
for paving purposes, the petroleum in use, on careful evaporation 
at 400° F., left a residuum of solid bitumen amounting to 61.1 per 
cent, and penetrating 59°, as appears in the preceding table, whereas 
industrially only 33 per cent was recovered having about the same 
penetration. The physical characteristics and proximate com- 
position of the industrial product obtained in this way are given 
in the accompanying tables. See pages 258, 259, 260, 261 , and 262. 



258 



THE MODERN ASPHALT PAVEMENT. 

"DEGRADE CALIFORNIA ASPHALT— PHYSICAI 



Test number 

Year received 

PHYSICAL PROPERTIES. 

Spepific gravity 78° F./78° F. t original substance, dry 

Color of powder or streak 

Lustre 

Structure 

Fracture 

Hardness, original substance 

Odor 

Softens , 

Flows 

Penetration at 78° F 

CHEMICAL CHARACTERISTICS. 

Loss, 325° F., 7 hours 

Residue penetrates at 78° F 

Loss, 400° F., 7 hours (fresh sample) 

Residue penetrates at 78° F 

Bitumen soluble in CS 2 , air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 

This is per cent of total bitumen. 

Per cent of soluble bitumen removed by H 2 S0 4 

Per cent of total bitumen as saturated hydrocarbons 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air tempera 
ture 

Bitumen yields on ignition : 

Fixed carbon 



18250 
1898 



1.089 

Black 
Lustrous 
Uniform 
Conchoidal 

-1 
Asphaltic 

150° F. 

162° F. 
25° 



.83% 
17° 

4.9% 
9° 

98.3% 
0.5 
1.2 



100.0 



65.0% 
68.6 
50.0 
33.1 



7.0 

19.0% 



It will be noted by a comparison of the above data with 
those given on page 257 that while the solubility of the bitumen 
in carbon disulphide is unaltered in the process of distillation a 
very considerable portion of it has often been rendered insoluble 
in oold carbon tetrachloride and in 88° naphtMa. At the same 
time the amount of fixed carbon in the industrial product is largely 



RESIDUAL PITCHES. 
CHARACTERISTICS AND PROXIMATE COMPOSITION. 



259 



68488 


69549 


69550 


69605 


69606 


1903 


March 1904 


March 1904 


April 1904 


April 1904 


1.062 

Black 

Lustrous 

Uniform 

Sticky 

Tacky 

Asphaltic 

142° F 

156° F„ 

52° 


1.052 

Black 
Lustrous 
Uniform 

Sticky 

Tacky 
Asphaltic 

178° F. 

190° F 

45° 


1.046 

Black 
Lustrous 
Uniform 

Sticky 

Tacky 
Asphaltic 

106° F. 

120° F, 

65° 


1.055 

Black 

Lustrous 

Uniform 

Sticky 

Tacky 

Asphaltic 

128° F. 

141° F. 

50° 


1.071 

Black 

Lustrous 

Uniform 

Conchoidal 

-1 

Asphaltic 

120° F. 

135° F. 

52° 


83% 
Hard 


2.7% 
Hard 


• 94% 
33° 


2.1% 
23° 


2.7% 
29° 


6.2% 
Hard 


9.6% 
Hard 


8.4% 
8° 


6.7% 
10° 


7.1% 
16° 


99.3% 
.4 
.3 


99.2% 

.8 
Trace 


99.6% 
.4 
.0 


99.6% 
.3 
.1 


99.7% 

.3 
Trace 


100.0 


100.0 


100.0 


100.0 


100.0 


77.0% 
77.5 
47.8 
40.5 


66.6% 
67.0 
56.9 
28.9 


70.5% 
70.8 
62.7 
26.4 


68.5% 
68.8 
57.7 
29.2 


70.0% 

72.2 

57.3 

42.8 


0.5% 


7.3% 


2.8% 


2.2% 


6.0% 


15.0% 


18.0% 


16.7% 


18.0% 


18.8% 



increased and this increase corresponds to the degree of severity 
of the heat to which the oil has been subjected. These differ- 
ences characterize the California pitches as being, to a certain 
extent, products of decomposition and on this account undesirable 
material. 

Considered as a class they are also undesirable because they 



260 



THE MODERN ASPHALT PAVEMENT. 
"D» GRADE CALIFORNIA ASPHALT. 



Test number. . 

PHYSICAL PROPERTIES. 

Specific Gravity, 78° F./78° F., original sub 

stance, dry 

Color of powder or streak , 

Lustre 

Structure , 

Fracture 

Hardness, original substance 

Odor 

Softens 

Flows 

Penetration at 78° F 

CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss, 325° F., 7 hours 

Residue penetrates at 78° F 

Loss, 400° F., 7 hours (fresh sample) 

Residue penetrates at 78° F 

Bitumen soluble in CS^ air temperature 

Difference 

Inorganic or mineral matter 

Malthenes : 

Bitumen soluble in 88° naphtha, air tem- 
perature 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 
H 2 S0 4 

Per cent of total bitumen as saturated hy- 
drocarbons 

Bitumen soluble in 62 c naphtha. 

This is per cent of total bitumen 

Carbenes : 

Per cent of bitumen insoluble in carbon 
tetrachloride, air temperature 

Bitumen yields on ignition: 

Fixed carbon 



18250 


68488 




More 


Carelessly- 
Prepared 


Carefully 
Prepared 


1.089 


1.062 


Black 


Black 


Lustrous 


Lustrous 


Uniform 


Uniform 


Conchoidal 


Tacky 


-1 

Asphaltic 
150° F. 


Sticky 

Asphaltic 

142° F. 


162° F. 


156° F. 


25° 


52° 


.83% 
17° 


.83% 
Hard 


4.9% 
9° 


6.2% 
Hard 


98.3% 
0.5 


99.3% 
.4 


1.2 


.3 


100.0 


100.0 


65.0% 
68.6 


77.0% 

77.5 


50.0 


47.8 


33.1 


40.5 





80.2% 
80.8 


7.0% 


0.5% 


19.0% 


15.0% 



RESIDUAL PITCHES. 



261 



are not uniform in character, as shown by the different degree 
of solubility of the bitumen in cold carbon tetrachloride and by 
the very considerable variation in the amount of fixed carbon 
which they yield. 

"D" GRADE ASPHALT FROM REFINERY AT LOS ANGELES, CAL. 
AVERAGE AND EXTREMES OF COMPOSITION IN 1904. 



PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Flashes, ° F., N. Y. State oil-tester 

Softens 

Flows 

Penetration at 78° F 

CHEMICAL CHARACTERISTICS. 

Loss, 400° F., 4 hours 

Residue after heating penetrates at 78° F.. . . 

Bitumen soluble in CS a , air temperature 

1 Hfierence ." 

Inorganic or mineral matter 

Malthenes : 

Per cent of total bitumen soluble in 88° 
naphtha, air temperature 

Carbenes : 

Insoluble in carbon tetrachloride, air tem- 
perature 

Number of runs 



Average. 



1.060 
406° F. 
137° F. 
150° F. 
56° 



7.12% 
14° 

99.4% 
.4 
.2 

100.0 
71.61% 

4.37% 
565 



Highest. 



1.066 
420° F. 
130° F. 
180° F. 
118° 



9.40% 
15° 

99.9% 
1.59 
.54 



83.81% 



6.91% 



Lowest. 



1.054 
385° F. 
124° F. 
140° F. 

24° 



5.52% 
12° 

08.1% 
.0 
.0 



66.01% 



.32% 



From an average of a very large number of analyses of " D " 
grade asphalts it has been found that the amount of fixed carbon 
which they yield, when prepared as carefully as possible by the 
present industrial process, does not vary far from 15 per cent, 
although at times it reaches 19 per cent where the product is care- 
lessly handled, and should not exceed 10 per cent as shown by 
our laboratory results. This characteristic of the California 
pitches is important in differentiating them from those made 



262 



THE MODERN ASPHALT PAVEMENT. 



from Texas oil, which yield a much higher percentage of fixed 
carbon. 

"D" GRADE CALIFORNIA ASPHALT. BITUMEN INSOLUBLE IN 
CARBON TETRACHLORIDE. 





Bitumen Insolu- 


Test Number. 


ble in Carbon 
Tetrachloride, 




Air Temperature. 


18250 


7-0% 


63847 


.5 


69549 


7.3 


73798 


.6 


73799 


.4 


73800 


.3 


73801 


.1 


73959 


.2 


73960 


.1 


73961 


.1 


73962 


.2 


74087 


.2 


74088 


2.8 


74089 


.1 


74090 


.2 


74091 


1.3 



For the purpose of preparing a pitch suitable for paving pur- 
poses it is, of course, desirable that some of the malthenes should 
be converted to asphaltenes, although not to carbenes. The bitu- 
men, soluble in 88° naphtha, should be reduced to about 70-75 
per cent and the fixed carbon should reach 15 per cent. 

Harder Residual Pitches. — Where the consistency of the 
asphaltic residue is harder, its character has been denominated 
by other letters than " D." For example, A, B, and C grades 
are found, and much of the " D " grade put upon the market 
corresponds to these materials rather than to a true " D " grade. 
"Where an attempt is made to manufacture the different grades 
they are expected to be of a consistency corresponding to the 
following penetrations on the Bo wen scale: 

A Grade 9° 

B " 15° 

C " 25° 

D " 46° and above. 



RESIDUAL PITCHES. 263 

Residual bitv.mens having a penetration of less than 46° are 
deficient in the less viscous malthenes and require a very large 
amount of flux, to bring them to a proper consistency for paving 
cement. This results in the presence of too large a percentage 
of both brittle asphaltenes and the lighter forms of malthenes. 
Where these very hard residual pitches are in use in the produc- 
tion of a paving cement the results have been disastrous in climates 
where severe conditions are met, although they may be passable 
in the climate of Southern California. 

Of late years, the use of such very hard residual pitches has 
been done away with, and those which are used for paving purposes 
are now very skilfully prepared at low temperatures, of very nearly 
the proper consistency for use as a paving cement, so that it is 
not necessary to add more than two or three pounds of flux, and 
often none at all, before using the bitumen. 

" Specifications for ' P ' Grade Asphalt. — ' D ' grade asphalt 
should be the residue from the careful distillation, with steam 
agitation, of some suitable California petroleum at as low a tem- 
perature as possible and certainly not exceeding 700° F. It shall 
be free from free carbon or suspended insoluble matter, which 
are evidences of excessive cracking. 

" It shall be soluble to the extent of at least 98 per cent in 
carbon disulphide, 95 per cent in cold carbon tetrachloride and 
not less than 65 nor more than 80 per cent of it shall be solu- 
ble in 88° Pennsylvania naphtha, preferably nearer the former 
figure. 

" It shall not flash below 450° F. and shall have a density be- 
tween 1.04 and 1.06. It shall not volatilize more than 8.0 per cent 
at 400° F. in 4 hours, and shall have a penetration between 40° 
and 70°. It shall melt at not less than 140° nor over 180° F. on 
mercury, according to the method in use in the New York Test- 
ing Laboratory, and shall yield not more than 15 per cent of 
fixed carbon on ignition. 

" It shall have a consistency of not less than four (4) milli- 
meters penetration at 78° F. when tested for five (5) seconds with 
a No. 2 needle weighted with 100 grams." 

The lower the temperature at which the asphalt is produced 
the smaller the percentage of cracked products it will contain 
and the smaller the loss will be on heating for 4 hours at 400° F. 



264 



THE MODERN ASPHALT PAVEMENT. 



The difference in its character when run down in 20 and 65 hours 
can be seen from the following figures: 

COMPARISON BETWEEN "D" GRADE TAKING 65 AND 20 
HOURS TO COME TO GRADE. 



Hours to grade 

Still 

Bitumen Boluble in CS 2l air temperature 

Difference 

Inorganic or mineral matter 

Malthenes: 

Bitumen solution in 88° naphtha, air temp. . . 
This is per cent of total bitumen 

Penetration of still sample at 78° F 

" " barrelling sample at 78° F 

Specific gravity 78° F./78° F 

Softens 

Flows f 

Loss, 400° F., 4 hours. 

Penetration, at 78° F., of residue after heating 

Yield 



20 



Small 



99.65% 
.25 
.10 


99.90% 
.10 
.00 


100.00 


100.00 


71.77% 
72.02 


72.50% 
72.57 


70° 
70° 


66° 
69° 


1.057 


1.054 


120° F. 
138° F. 


124° F. 
140° F. 


9.4% 


6.8% 


12° 


15° 


33.0% 


43.5% 



65 



Large 



For comparison with the preceding " D " grade product a 
bitumen procured on the market in Los Angeles, Cal., in 1904, 
will serve. See table on page 265. 

Here the percentage of fixed carbon is very high and that of 
the malthenes is low, the total bitumen at the same time amount- 
ing to only 93 per cent, while a very large proportion of bitumen 
soluble in carbon disulphide but insoluble in cold carbon tetra- 
chloride and of free carbon are present. This material has been 
plainly overheated and it will require from 30 to 40 pounds of flux 
instead of the much smaller quantity necessary with a properly 
prepared asphalt. In this connection it may be of interest to 
remark that the hardness of a " D " grade asphalt is proportional, 
as in the native bitumens, to the percentage of naphtha soluble? 
bitumen which it contains as appears from the following deter 



RESIDUAL PITCHES. 



255 



"D" GRADE ASPHALT FROM AN ASPHALTUM OIL AND 
REFINING CO. 

PHYSICAL PROPERTIES. 

Test number 69014 

Specific gravity, 78° F./78° F., original substance, dry ..... . 1 .077 

Softens . . 195° F. 

Flows 205° F. 

Penetration at 78° F 27° 

CHEMICAL CHARACTERISTICS. 

Original substance: 

Loss, 212° F., 1 hour 0.0% 

Dry substance: 

Loss, 325° F., 7 hours 1.3% 

Character of residue Surface 

smooth. 

Loss, 400° F. , 7 hours, additional loss 5.3% 

Character of residue. . . Shrivelled 

surface, 
penetration 

5°. 

Bitumen soluble in CS 2 , air temperature 92 . 6% 

Difference (largely carbon) 7.3 

Inorganic or mineral matter .1 

100.0 
Malthenes : 

Bitumen soluble in 88° naphtha, air temperature 64 .4% 

This is per cent of total bitumen 69 . 5 

Bitumen soluble in 62° naphtha 65 . 6% 

This is per cent of total bitumen 70 . 8 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature 13.1% 

Bitumen yields on ignition : 

Fixed carbon 19 .0% 

Remarks: A small amount of suspended matter is noted under the 
microseope. 



266 



THE MODERN ASPHALT PAVEMENT. 



minations on the products produced at one plant under the same 
conditions : 



Number 


103 
31° 

66.0% 


104 
53° 

70.6% 


105 
54° 

70.6% 


106 


Penetration at 78° F 

Naphtha soluble bitumen. . . 


87° 

72.4% 



Asphaltic Residues from Texas Oil. — The semi-asphaltic oil 
from the Beaumont field in Texas leaves a residue of solid bitu- 
men on distillation which, however, as in the case of California 
oil, varies in character according to the method of distillation 
employed. In the case of California oils, with careful distillation 
a larger percentage of residue was obtained than was the case indus- 
trially. With the Beaumont oil the reverse is the case; on dis- 
tillation in vacuo but 9.0 per cent of solid bitumen was recovered 
while industrially as much as 30 per cent is obtained. This is, 
probably, due to the fact that condensation goes on in the case 
of the Beaumont oil instead of cracking as in the case of California 
petroleum. Analyses of residual pitches from Texas petroleum 
representing the product as turned out in 1903 and again in 
1907, are given on the opposite page, the two materials originat- 
ing from different manufacturers. 

An examination of the preceding results shows that the dis- 
tillation has been earned much further than is the case in the 
production of the California asphalts. This is evidenced by the 
greater density of the product and the very much higher per- 
centage of fixed carbon which it yields. It should also be noted 
that the two forms of residual pitch are differentiated by the fact 
that that from the Texas oil contains a larger percentage of satu- 
rated hydrocarbons than that from the California oil, a fact which 
might be expected as the stability of the former is much greater 
than that of the latter, owing to the amount of paraffine hydro- 
carbons which it contains. The asphaltic residue from the Texas 
oil is marked by the presence of a little over 1 per cent of paraffine 
scale, but the amount is insufficient to give it the character of a 
paraffine material. 

The residual pitches from Texas oil are no more uniform in 



RESIDUAL PITCHES. 



267 



RESIDUAL PITCH FROM TEXAS PETROLEUM. 



Test number ,. 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original sub- 
stance, dry 

Color of powder or streak 

Lustre 

Structure 

Fracture 

Hardness, original substance 

Odor 

Softens 

Flows 

Penetration at 78° F., Bowen 

Penetrometer at 78° F 

CHEMICAL CHARACTERISTICS. 

Dry substance: 

Loss 325° F., 7 hours 

Loss 400° F., 7 hours 

Bitumen soluble in CS 2 , air temperature . . 

Inorganic or mineral matter 

Difference 

Malthenes : 

Bitumen soluble in 88° naphtha, air temp. 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by 

H 2 S0 4 

Per cent of total bitumen as saturated 

hydrocarbons 

Bitumen soluble in 62° naphtha 

This is per cent of total bitumen , 

Carbenes: 

Bitumen insoluble in carbon tetrachloride, 
air temperature , 

Bitumen yields on ignition: 

Fixed carbon , 

Paraffine scale - 



1903 
68943 



1.0803 


1.0703 


Black 


Black 


Lustrous 


Lustrous 


Uniform 


Uniform 


Semi-conchoidal 


Conchoidal 


-1 


-1 


Asphaltic 


Petroleum 


230° F. 


143° F. 


247° F. 


164° F. 


13° 


18° 




7° 


.13% 


.95% 


.19 


1.22 


99.0% 


98.2% 


.2 


Trace 


.8 


1.8 


100.0 


100.0 


65.4% 


69.6% 


66.1 


70.9 


32.1 


51.1 


44.8 


65.6 


71.5% 


70.1% 


72.2 


71.4 



5.1% 

24.0% 
1.2% 



1907 
102529 



14.6% 

19.5% 
.8% 



268 



THE MODERN ASPHALT PAVEMENT. 



character than those prepared from California petroleum and, no 
doubt, for the same reason. That they are very variable in char- 
acter can be seen from the results of an examination of five 
samples, taken from one delivery, which were submitted to the 
author for examination. 

RESIDUAL PITCH FROM BEAUMONT, TEXAS, PETROLEUM 
TAKEN FROM ONE DELIVERY. 



Test number 


72550 

10° 

None 

98.1% 

1.8 

.1 


72589 

16° 
None 

97.7% 

2.2 

.1 


72590 

93° 

100.0% 

99.3 
.4 
.3 


72591 

58° 
76.0% 

99.0 
.9 
.1 


72592 


Penetration at 78° F./78° F 

Flow 


81° 
86.0% 

99.1 


Bitumen soluble in CS 2 


Difference 


5 


Inorganic or mineral matter 


.4 


Carbenes: 

Bitumen insoluble in carbon 
tetrachloride, air temperature. 

Bitumen yields on ignition: 

Fixed carbon 


100.0 
10.5% 


100.0 

12.7% 
23.0% 


100.0 

6.7% 


100.0 
7.0% 


100.0 
6.7% 









In this delivery material was found which was so hard as to 
hardly flow at 212° F. (No. 72550) and so soft as to be readily 
melted (No. 72590). 

Other lots which have been examined by the author have 
shown an equal lack of uniformity, as can be seen from the follow- 
ing figures: 

RESIDUAL PITCH FROM BEAUMONT, TEXAS, PETROLEUM. 



Test number 

Penetration at 78° F./78° F 

Bitumen soluble in CS 2 , air temperature. . . 

Malthenes : 

Bitumen soluble in 88° naphtha, air tempera- 
ture 

This is per cent of total bitumen 



Carbenes : 

Bitumen insoluble in carbon tetrachloride 
air temperature 



Bitumen yields on ignition: 
Fixed carbon 



63526 


63527 


Too soft 


110° 


98.3% 


96.6%. 


78.2% 
79.6 


72.2% 
74.7 


8.6% 


12.8% 


14.5% 


17.6% 



63528 

15° 

95.7% 



67.9% 
71.0 



12.5% 
21.1% 



RESIDUAL PITCHES. 



269 



The most important characteristic of the residual pitches from 
Texas oil is that they yield, as prepared, and as found on the 
market, more than 20 per cent of fixed carbon as compared with 
15 per cent for the California pitches. This characteristic while 
it may be due somewhat to the fact that the Texas pitch is a denser 
material, because the distillation has been carried to a point beyond 
that to which the California oil is submitted, is an important one 
industrially as it makes it possible to differentiate and determine 
the origin of any of these forms of bitumen. The two can also be 
differentiated by determining whether paraffine is present, none 
being found in the California products and about 1 per cent in 
those from Texas. 

Examples of the variation in the character of Texas residual 
pitches as revealed by the percentage of carbenes which they con- 
tain is shown by the following analyses: 

RESIDUAL PITCHES FROM BEAUMONT, TEXAS, PETROLEUM. 





Bitumen Insolu- 


Test Number. 


ble in Carbon 




Tetrachloride, 




Air Temperature. 


63526 


8.6% 


63527 


12.8 


63528 


12.5 


68943 


5.1 


69015 


5.1 


72550 


10.5 


72589 


12.7 


72590 


6.7 


72591 


7.0 


72592 


6.7 



The amount is generally much larger than is found in the more 
carefully prepared California "Degrade asphalt and points to 
overheating in the preparation of these particular specimens. 
This is much greater in the pitch which has been produced in 1907 
than in the supply of 1903. The material has recently been of 
very poor quality, and, in the opinion of the author, it is entirely 
unsuitable for use in the paving industry. 



270 



THE MODERN ASPHALT PAVEMENT. 



Ebano Asphalt. — A residual pitch made from the asphaltic 
oil or maltha occurring at Ebano, Mexico, about thirty miles 
from Tampico, on the line of the Mexican Central Railroad, has 
been on the market in the United States and abroad, for a few 
years, under the designation of " Ebano Asphalt," a well sunk 
at that point to a depth of 1600 feet, producing from 1200 to 
1500 barrels of petroleum a day. It corresponds in its preparation 
and characteristics to the California residual pitches. Following 
are the results of examinations of various grades of the material: 



Test number 
Identified as 



PHYSICAL PROPERTIES. 



Penetration at 78 c 

Softens 

Flows 



F. — Bowen 



CHEMICAL CHARACTERISTICS. 



Bitumen soluble in CS 2 , air temp. 

Inorganic or mineral matter 

Difference 



Carbenes: 

Bitumen insoluble in carbon tetra- 
chloride, air temperature 

Malthenes : 

Bitumen soluble in 88° naphtha, air 

temperature 

This is per cent of total bitumen 
Per cent of soluble bitumen removed 

byH 2 S0 4 

Bitumen yields on ignition: 

Fixed carbon 

Paraffine scale 



102261 
"E" 


102262 
"DX" 


102263 
"D" 


62 
125° F. 
163° F. 


30 
185° F. 
200° F. 


26 
190° F. 
206° F. 


99.4% 
.1 
.5 


97.9% 

.2 

1.9 


97.8% 
none 
2.2 


100.0% 


100.0% 


100.0% 


•4% 


14.4% 


15.5% 


69.0% 
69.4 


66.0% 
66.5 


55.5% 
56.3 


89.0 


91.0 


92.0 


19.2% 
1.0% 


23.9% 
1.3% 


24.9% 
1.3% 



102264 
"B" 



7 
260° F. 
278° F. 



95.8% 
.3 
3.9 



100.0% 
19.7% 



48.1% 
50.2 

93.0 

30.5% 
1.9% 



Where the Ebano asphalt is made of "E" grade consistency, 
it seems to be of a character as good as that of the same material 
made in California, but where the distillation has been carried to 
such a point that the consistency is much harder, the percentage 
of carbenes present shows that the bitumen has been, at least 
in some cases, very seriously decomposed and such a product 
is, on this account, very unsatisfactory. 

Baku Pitch. — On the Continent a residual pitch from the 
distillation of Russian petroleum is an industrial product. This 
has the following composition: 



RESIDUAL PITCHES. 271 

BAKU PITCH. 
Test number 63200 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 1 . 1098 

Color of powder or streak Black 

Lustre Lustrous 

Structure Uniform 

Fracture Semi- 

conchoidal 
Hardness, original substance — 1 

Odor Petroleum 

Softens 140° F. 

Flows 150° F. 

Penetration at 78° F 10° 

CHEMICAL CHARACTERISTICS. 

Bitumen soluble in CS 2 , air temperature 91 . 6% 

Difference 8.4 

Inorganic or mineral matter Trace 

100.0 
Malthenes : 

Bitumen soluble in 88° naptha, air temperature 54. 6% 

This is per cent of total bitumen 59 . 6 

Per cent of soluble bitumen removed by H 2 S0 4 44 . 1 

Per cent of total bitumen as saturated hydrocarbons 33 . 3 

Bitumen soluble in 62° naphtha 61 . 3% 

This is per cent of total bitumen 66 . 9 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temp 10 . 4% 

Bitumen yields on ignition: 

Fixed carbon 26.8% 

Paraffine scale 1 . 7% 

This pitch has a comparatively high density, yields a large per- 
centage of fixed carbon, bitumen insoluble in cold carbon tetra- 
chloride and much organic matter not bitumen; showing that the 
distillation has been pushed to an extreme. It contains 1.7 percent 
of paraffine scale. It is a remarkable fact that the softening-point 
of this material is much nearer that of the California residue than of 



272 THE MODERN ASPHALT PAVEMENT. 

that from Beaumont, Texas, oil. It might, perhaps, be possible 
to use a small amount of this bitumen in the paving industry as 
an amendment to some asphalts. 

Solid Bitumens the Product of the Condensation of Heavy 
Oils. — Another class of bitumens are the artificial ones obtained 
by the treatment of any of the fluxes which have been described 
with sulphur or oxygen at high temperatures. In their uses and 
consistency they may be ranked between the fluxes and the solid 
bitumens. 

Pittsburg Flux. — The first bitumen of this description to be 
put upon the market was known as Pittsburg Flux. It was made 
by adding to an ordinary Pennsylvania petroleum residuum about 
one pound of sulphur to every gallon of oil and heating the 
material to a point a little below that of distillation and main- 
taining it at that temperature until the evolution of hydrogen 
sulphide ceases. The residuum is, in this way converted into a 
semi-solid cheesy bitumen which is very short, that is to say, 
has little ductility, and is very slightly susceptible to changes of 
temperature. The reaction which takes place is represented by 
the following equation: 

C n H2 n + S = C n H n . 2 + H2S. 

The reaction, in reality, is not as simple as this but the result is 
explained as well. Two molecules are condensed to one with 
the accompanying evolution of hydrogen sulphide gas and with 
the resulting changes in the properties of the bitumen. The great 
expense incurred for sulphur in this process made it necessary to 
utilize the by-product of hydrogen sulphide. This was done by 
converting it into sulphuric acid. The business was not profitable 
even under these conditions and was soon abandoned. The mate- 
rial could not be used as the principal source of bitumen in making 
an asphalt cement, being too short, and only as an addition, in 
small amounts, to the ordinary asphalts. Used in this way it 
has been successful in one or two instances. 

An analysis of this material is presented in the table on page 275. 

Ventura Flux. — Later on an attempt was made to make a 
similar substance from the asphaltic petroleum of California. The 



RESIDUAL PITCHES. 273 

product was a slight improvement on the Pittsburg Flux but pave- 
ments made with it without the addition of native solid bitumen 
were failures in Allegheny, Pa. Its manufacture was abandoned 
after a few years. 

Byerlyte. — In the meantime Byerly, of Cleveland, had found 
that the oxygen of the air was as satisfactory a condensing agent 
as sulphur, imitating the practice of blowing certain vegetable 
and fish oils in order to thicken them and give them greater viscosity. 
He produced a substance similar to Pittsburg Flux by drawing 
air through residuum while the latter was maintained at a high 
temperature. Depending on the length of time during which 
the air was allowed to act the product was soft or as hard as pitch. 
This material has been used to some extent in making asphalt 
blocks in Washington, but even this use has now been abandoned. 
In mixture in small proportion with the native solid bitumens 
it can be used but there is no advantage in doing so commen- 
surate with the expense involved in the treatment of the original 
residuum. 

Hydroline " B." — Still more recently the asphaltic residuum 
from the asphaltic petroleums of Texas has been put upon the mar- 
ket, after having been blown, under the name Hydroline " B." 
It possesses in this form no qualities which could recommend it 
very strongly for paving purposes except, perhaps, as an amend- 
ment to certain inferior asphalts and it need hardly be considered 
here. 

Sarco Asphalt. — This material, which has recently been on 
the market, is a blown product like Hydroline "B," prepared 
from Kansas residuum, and it possesses much the same properties, 
having little ductility and being very short. 

A specimen recently examined in the author's laboratory, 
showed the following characteristics: 

Test number 96891 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F., original substance, dry 981 

Softens 190° F. 

Flows 210° F. 

Penetration at 78° F.— Bowen 120° 

Condition at 140° F. after 1 hour / S ,?^ 9 

\ slightly. 



274 THE MODERN ASPHALT PAVEMENT. 

CHEMICAL CHARACTERISTICS. 

Bitumen soluble in CS 2 , air temperature 99 . 1% 

Inorganic or mineral matter .7 

Difference .2 



Malthenes: 10 °° % 

Bitumen soluble in 88° naphtha, air temperature 69 .8% 

This is per cent of total bitumen 70 .4 

Carbenes : 

Bitumen insoluble in carbon tetrachloride, air temperature .2% 

Bitumen yields on ignition: 

Fixed carbon 10.3% 

Paraffine scale 12.3% 

It is notable for the very high percentage of paraffine scale 

which it contains, which, in addition to the properties conferred 

by blowing the oil with air, adds to its shortness. It is made 

of several grades, having a penetration of from 50 to that of the 

sample which was examined. 

According to analyses made by Mr. Francis P. Smith, three 

specimens which he examined had the following properties: 

Test number 1175 1176 1210 

Melting-point, degrees F 171 188 198 

Penetration at 32° F.(Dow, 1 min., 200 gms.) ... 42 49 31 

Penetration at 77° F. (Dow, 5 sec, 100 gms.) ... 60 70 45 

Penetration at 115° F. (Dow, 5 sec, 50 gms.) . . 97 

Bitumen soluble in CS 2 98 .0% 

Organic insoluble 1.0 

Ash 1.0 

Naphtha soluble bitumen 79 .9% 

Naphtha soluble bitumen (per cent total bit.) . . 81 .5 

Loss on heating 5 hours at 325° F 08% 

Penetration after heating 60 

Ductility 3 cm. 

Fixed carbon 10.6% 

It is hardly possible that a satisfactory pavement could be 
made with such material, although it might be combined to a 
certain extent with the ordinary asphalts. 

The character of Pittsburg Flux, Byerlyte and Hydroline "B" 
is shown in the table on page 275. 

From these figures it appears that the materials are nearly 
pure bitumens and that, not having been subjected to suffi- 
ciently high temperatures to produce cracking, the amount of 
bitumen insoluble in carbon tetrachloride is practically nothing. 
According to their derivation the materials carry more or less 
paraffine but the Hydroline " B " being derived from a Texas oil 



85 


71 


97.7% 


98.7% 


1.8 


1.3 


.5 


Trace 


79.0% 


79.2% 


80.9 


80.3 


•4% 


.15% 


61 


33 


3 cm. 


2 cm. 


108% 


10.8% 



RESIDUAL PITCHES. 



275 



Test number 

Bitumen 

PHYSICAL PROPERTIES. 

Specific gravity, 78° F./78° F 

original substance, dry 

Color of powder or streak 

Lustre. 

Structure 

Fracture 

Odor 

Softens 

Flows 

Penetration at 78° F 

CHEMICAL CHARACTERISTICS. 

Dry substance : 

Loss, 325° F., 7 hours 

Character of residue 

Loss, 400° F., 7 hours (fresh 

sample) 

Character of residue 

Bitumen soluble in CS 2 , air temp 

Difference 

Inorganic or mineral matter 



Malthenes : 

Bitumen soluble in 88° naphtha, 
air temperature 

This is per cent of total bitumen 

Per cent of soluble bitumen re- 
moved by H 2 S0 4 

Per cent of total bitumen as sat- 
urated hydrocarbons 

Bitumen soluble in 62° naphtha 
This is per cent of total bitumen 

Carbenes : 

Bitumen insoluble in carbon te- 
trachloride, air temperature. 

Bitumen yields on ignition: 
Fixed carbon 

Paraffine scale 





6123 


6124 


Pittsburg 
Flux 


Byerlyte 

(paving) 


Byerlyte 
(roofing) 


.9879 


1.023 


.9070 


Black 


Black 


Black 


Dull 


Dull 


Dull 


Uniform 


Uniform 


Uniform 


Cheesy 
Petroleum 


Cheesy 
Petroleum 


Cheesy 
Petroleum 


295° F. 


245° F. 


230° F. 


353° F. 


294° F. 


254° F. 


74° 


63° 


107° 


1.7% 
Smooth 


• 93% 
Smooth 


1.8% 
Smooth 


4.4% 
Blistered 


5.9% 
Smooth 


6.5% 
Smooth 


99.7% 
.3 


99.7% 
.3 


99.0% 
.5 


.0 


.0 


.0 


100.0 


100.0 


100.0 


67.1% 
67.3 


62.0% 
62.2 


66.8% 
67.1 


14.8 


25.5 


17.4 


57.3 


46.3 


55.5 


71.5% 
71.7 


67.2% 
67.4 


72.0% 
72.3 


•3% 


• 4% 


• 3% 


14.7% 


18.0% 


14.3% 


10.3% 


4.6% 


5.7% 



71436 

Hydro- 
line "B" 



1.0043 

Black 

Dull 

Uniform 

Cheesy 

Petroleum 

206° F. 

220° F. 

55° 



1.0% 
Smooth 
penetra- 
tion, 45° 



5.8% 
Smooth 
penetra- 
tion, 40° 

99.9% 
.1 
.0 



100.0 



69.3% 
69.4 

12.7 

60.6 



•5% 

12.2% 
1.0% 



276 THE MODERN ASPHALT PAVEMENT. 

contains no more than is found in the residual pitch iron 
the same oil. It is worthy of remark as to Byerlyte that, 
although made from paraffine oil, it contains much less paraf- 
fine scale than would be expected, and would point to the fact 
that this material has become altered in the process of manu- 
facture. 

With none of these materials, as the principal constituent of 
a paving cement, is it possible to produce a satisfactory surface 
mixture. They are all too short, but they may be used as an 
amendment in an amount not exceeding 10 per cent. Owing to 
the fact of their great lack of susceptibility to change in con- 
sistency within wide ranges of temperature they present some 
advantages. 

Differentiation of the Residual Pitches from the Natural 
Asphalts. — The residual pitches, it appears from the preceding 
data, contain practically no mineral matter. With only one excep- 
tion there is no native bitumen in use in the asphalt paving indus- 
try which has the same characteristic. It is, therefore, possible 
to differentiate, except in the case of gilsonite, an oil asphalt, 
so-called, from a native bitumen by determining the amount of 
mineral matter present. The mineral matter in the latter is 
generally of a ferruginous nature while that derived from the 
native bitumens generally contains silica. A microscopic exam- 
ination of the residue left on ignition will, therefore, aid in the 
determination. Even in the case of gilsonite the color of the 
ash is quite different from that obtained from the residual pitches. 
Unfortunately the amount of fixed carbon which the California 
" D " grade asphalt yields and that from the native bitumens 
is so nearly the same that this characteristic cannot be success- 
fully used, although the amount obtained may be of value as 
indicating the presence of grahamite which in itself has a high 
fixed carbon. The native bitumens carry, however, less bitu- 
men insoluble in cold carbon tetrachloride but soluble in carbon 
disulphide than the residual pitches, unless the latter are very 
carefully made, and in case of doubt the differentiations of the 
two classes of materials may be assisted by comparative deter- 
minations of this form of bitumen. 

SUMMARY. 

All petroleums on evaporation under suitable conditions leave 
a pitchy residue. The residue from the asphaltic or semi-asphaltic 



RESIDUAL PITCHES. 277 

petroleums resembles the native asphalts. The principal supplies 
available for use in the paving industry are residual pitches from 
California and from Texas oil. These are each made in such a 
careless way that they consist largely of alteration products of 
the original hydrocarbons as shown by the lack of solubility of 
some of their constituents as compared with those found in the 
original oil. On this account the material is not always satisfac- 
tory and, moreover, requires great skill to use it. 

The residual pitches from Texas and from California oils can 
be readily differentiated by certain characteristics, that from the 
Texas oil generally yielding a higher percentage of fixed carbon 
than the pitch obtained from the California oil. 

The blown or oxidized petroleum residues are characterized 
by their lack of susceptibility to temperature changes, but are 
extremely short, which prevents their use as the main source of 
bitumen in the paving mixture. Pavements laid with them have 
generally eventually proved failures. They may possess some 
desirable qualities as an amendment to the native asphalt to 
an extent not exceeding 10 per cent, and, used in this way, should 
be considered as fluxes. 



CHAPTER XIV. 

COMPARISON OF VARIOUS NATIVE ASPHALTS AND THEIR 
RELATIVE MERITS FOR PAVING PURPOSES. 

In attempting to form an opinion on the availability of any 
native bitumen for paving purposes a number of things must be 
taken into consideration, which may be tabulated as follows: 

1. The quantity available. 

2. Its uniformity in character. 

3. Its stability in a melted condition at high temperatures. 

4. Its stability in consistency at the extremes of temperature 
which it meets in an asphalt pavement. 

5. The proportion of malthenes to asphaltenes which it con- 
tains. 

6. The proportion of flux which is required to make an asphalt 
cement. 

7. Mineral matter present and its character. 

i. The Quantity Available. — No native bitumen can be of any 
great importance in the paving industry without a large supply 
of it is available. Pavements can no doubt be constructed of a 
bitumen of which not more than 500 to 1000 tons can be gathered 
together with difficulty in any one year, but such supplies are too 
unreliable to permit of their being of permanent interest. There 
are hundreds of such deposits in which many thousands of dollars 
have been sunk without any adequate return for the investment. 
A deposit to be of any great value should afford a supply of at 
least 50,000 tons annuaUy without difficulty. The first thing 
to be done, therefore, in considering the availability of native bitu- 
men is to learn whether the deposit is such that the amount which 

278 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 279 

can be obtained from it will prove large enough to be of industrial 
importance. 

2. Its Uniformity in Character. — A great consideration in the 
turning out of a regular asphalt surface mixture is that the bitu- 
men from which it is made shall be of such a nature that every 
cargo or shipment of it may be exactly like all others. If this 
is not the case each lot will, of necessity, require a different method 
of handling, which necessitates great experience and skill which 
are not always to be found among those who are engaged in the 
laying of asphalt pavements. 

3. Its Stability in a Melted Condition at High Temperatures. — 
As the asphalt cement made from the native bitumens as they 
occur in the refined condition in the trade is necessarily main- 
tained in a melted condition at high temperature for considerable 
periods of time it is equally important that it should consist of a 
bitumen which does not become changed in consistency, under 
these conditions, owing to the rapid volatilization of certain of 
its constituents. 

There is a very decided difference in the behavior of different 
bitumens in this respect and this should be borne in mind in deter- 
mining whether one has a preference over another for use in the 
construction of asphalt pavements. 

4. Its Stability in Consistency at the Extremes of Tempera- 
ture which it Meets in an Asphalt Pavement. — There is a difference 
in the behavior of different bitumens, as far as their consistency 
is concerned, at the extremes of temperature which are met with 
in summer and winter, that is to say, some of them are much 
more susceptible to changes in consistency between very low and 
very high temperatures than others. This is an important con- 
sideration since, although a given bitumen may enable one to con- 
struct an asphalt surface which is of proper consistency at medium 
temperature, say 78° F., it may become extremely hard and brittle 
at zero or extremely soft and oily at 120° F., a temperature which 
asphalt surfaces frequently reach under our hot summer sun. 

5. The Proportion of Malthenes to Asphaltenes which it Con- 
tains. — The relative proportion of malthenes, those constitutents 
which are soluble in light petroleum naphtha, and of asphaltenes, 



280 THE MODERN ASPHALT PAVEMENT. 

the other constituents not soluble in this medium, has a bearing 
upon the availability of any native bitumen for paving purposes. 
Although to-day the deficiencies in this respect may be modified 
by the use of certain fluxes, which supply the missing constituents, 
this is not always the case and, when it is so, it requires very 
considerable skill to accomplish it. This has been illustrated more 
fully in another place. 1 

6. The Proportion of Flux which is Required to Make an 
Asphalt Cement. — The question of the amount of flux which is 
necessary to use with any bitumen is one of importance. If the 
native bitumen is so hard as to require a very large percentage 
of flux there is a very great probability, although this is not uni- 
versally the ease, that the resulting cement will be too oily and 
too susceptible to high temperature. 

Gilsonite is a bitumen which is an exception to this rule. To 
flux this material in making an asphalt cement, about equal parts 
of it and of heavy asphaltic oil are necessary, but the cement 
contains normal proportions of malthenes soluble in 88° naphtha, 
and of asphaltenes insoluble. Such a cement has an extremely 
rubbery consistency and a considerable amount of elasticity, 
a cylinder of the cement springing back to its original formation 
when bent nearly double. Such a cement, in addition, is not as 
susceptible to temperature changes as those made from the ordi- 
nary asphalts. A statement in regard to the relative proportions 
of various fluxes which must be combined with the various asphalts 
to produce cements of different penetrations is given on page 308. 

7. Mineral Matter Present and its Character. — The mineral 
matter present in any native bitumen may be desirable or unde- 
sirable. If it contains so much or if it is so coarse as to render 
it impossible to maintain it uniformly in suspension in the melted 
asphalt cement which is prepared from the bitumen it is undesir- 
able. If, on the other hand, it is extremely fine and acts as a 
filler, as in the case of Trinidad asphalt, it is very desirable. 

The fact that it may reduce the percentage of bitumen present 
is of no importance, since in the case of an asphalt consisting of 

1 See pages 139 and 178. 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 281 

99 per cent of bitumen it will be necessary in building up a satis- 
factory surface mixture to add a certain amount of filler which 
cannot be done as successfully by any artificial means as is done 
by nature. 

In this connection the following correspondence between the 
President of the Board of Public Works of a western city and a 
local chemist, many years ago, may prove of interest as well as 
the latter's answers to several other questions which are frequently 
asked. 

" May 22, 1893. 

"Dear Sirs: — A discussion has been going on in this city, 
which the citizens are largely interested in, in regard to asphalt 
paving. 

" It is claimed on one hand that asphalt is asphalt, no matter 
where it is found, and the only difference in asphalts is in the 
amount of bitumen which they contain. As a well-known and 
practical chemist in this city, I would thank you to answer the 
following questions, and send me a bill for your expert opinion. 

" 1. Does the percentage of bitumen determine the value 
of an asphalt for paving purposes? 

" 2. May or may not an asphalt contain a very large percent- 
age of bitumen and still be worthless for paving purposes? 

"3. Might or might not an asphalt, which in its natural state 
is good for paving purposes, be so destroyed by heat that it is 
practically worthless for paving purposes, and still the material 
after subjection to heat, be asphalt? 

" 4. Might or might not two asphalts contain the same amount 
of bitumen, and one be so unstable that it will not stand expo- 
sure to the sun, and the other be comparatively permanent? 

" 5. Is it possible that one asphalt might contain twice as 
much bitumen as another, and still be far inferior for street con- 
struction to the one containing a less quantity? 

"6. Is there any real system by which a chemist can tell to a 
certainty, by analysis, whether a given asphalt which has never 
been tried will make as good, permanent, and durable a pave- 
ment as another which has proved a success? 

" 7. Are there or are there not qualities required of an asphalt 



282 THE MODERN ASPHALT PAVEMENT. 

for paving purposes which makes it impossible for a chemist who 
has not made the subject a special study , to state for a certainty 
whether a given untried asphalt will make as good a pavement 
as another asphalt which has proved a success? 

" 8. What is the real test of standard or quality which will 
give the value of an asphalt for paving purposes? 

" 9. Might an asphalt pavement stand for one or two years, 
and fail from effect of elements in succeeding years, and might 
two asphalts stand equally for two years and show marked differ- 
ences in wear in succeeding years? 

" An early reply will oblige, 

" Yours respectfully, 

(Signed) "President Board of Public Works/! 

In reply to the above questions the following opinion was 
rendered : 

" 1st Answer. The percentage of bitumen does not determine 
the value of an asphalt for paving purposes. 

" 2d Answer. An asphalt might contain a very large percentage 
of bitumen, and still be comparatively worthless for paving pur- 
poses. 

" 3d Answer. An originally good asphalt for paving purposes 
might be so altered by heat as to be practically worthless, and yet 
the altered material would still be asphalt in the sense that it could 
not be distinguished from asphalt, notwithstanding its marked 
inferiority to the particular asphalt from which it was produced. 

" 4th Answer. Two asphalts might contain the same amounts 
of bitumen and yet possess entirely different powers of resistance 
to the destructive action of the elements. One might thus 
be comparatively permanent and stable, and the other greatly in- 
ferior. 

" 5th Answer. As the percentage of bitumen in an asphalt 
does not determine its value for paving purposes, it is quite pos- 
sible for one asphalt to contain a much higher percentage than 
another and yet be decidedly inferior for making a durable pave- 
ment. 

" 6th Answer. There is no system of chemical analysis that will 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 283 

determine for a certainty that a given untried sample of asphalt 
will make, in every way, as good a pavement as another asphalt 
which has proved a success. 

" 7th Answer. The requirements of an asphalt for paving 
purposes are of such a peculiar nature that it would be impossible 
for a chemist who had not made the subject a special study to 
state with certainty, from the results of analysis, whether or not a 
given sample would make as good a pavement as an asphalt which 
has proved a success. 

" 8th Answer. The real and final test of the quality of an 
asphalt for paving purposes is actual trial for a proper length of 
time. Proper chemical and physical tests of a new variety of 
asphalt may strongly indicate its probable value as a paving mate- 
rial, but these tests, though of great assistance in forming an 
opinion, really only show the advisability of submitting the asphalt 
to the final and infallible test of actual trial. 

" 9th Answer. A test of one or two years under any condition 
demonstrates only that that particular asphalt pavement is good 
for that length of time under those conditions, and does not demon- 
strate how much longer it will last under the same conditions or 
whether it will last as long under other or more unfavorable con- 
ditions. Two asphalt pavements might endure equally well for 
a given short time, and yet show decided difference under a long 
trial. 

" Having thus briefly answered the questions asked it may, 
perhaps, be well to give some explanation of the subject, in order 
to indicate the reasons for. the opinions expressed. First of all, 
it may be stated that asphalt is not a chemical compound or mineral 
of fixed and invariable composition. According to Dana it is a 
mixture of hydrocarbons, and the asphalts of different localities 
have various compositions. Mineralogically, bitumen is simply 
another name for asphalt or asphaltum. In paving parlance, 
however, bitumen has come to mean only the pure portion, so to 
speak, of the asphalt, the latter term being applied to the entire 
mixture of earthy and other impurities with the true bitumen. 
This view of bitumen having evidently been taken in the ques- 
tions asked, it was similarly considered in the replies. It is to 



284 THE MODERN ASPHALT PAVEMENT. 

be understood, then, that asphalt is an impure bitumen, and that 
bitumen is the pure article considered by Dana in his Mineralogy. 
But ; as before stated; bitumen has no fixed composition or com- 
bination of qualities. Its nature and physical properties are as" 
various as the localities where it is found. It can be no more 
strictly defined than coal. It is simply a mixture of various hydro- 
carbons, and may be either a solid or a liquid. Two bitumens of 
precisely similar percentage composition may have widely different 
properties, so that while one would furnish a most excellent paving 
material the other would be practically worthless. Such instances 
of substances of entirely dissimilar nature having the same per- 
centage composition abound in chemistry. Charcoal, the diamond, 
and plumbago, or black lead, may be mentioned as a familiar 
example. Light naphtha or gasoline and solid parafhne is another. 
It takes more than an ordinary chemical analysis to distinguish 
between such substances. Evidently, then, the mere percentage 
of bitumen in an asphalt would not determine its value for paving 
purposes, for this bitumen might have a consistency varying any- 
where from a non-cohesive liquid to a brittle worthless solid. By 
the action of the elements all asphalts undergo change. This 
change is due to oxidation, volatilization and other molecular 
disruption, and tends to produce greater solidification or apparent 
drying, and the asphalt may pass through all the stages of brittle- 
ness to final crumbling or disintegration. In all these stages the 
substance is still asphalt, although at many points it is evidently 
worthless as a paving material. While these changes are slow 
in nature, some of them may be greatly hastened by the applica- 
tion of heat, as in incautious or unskilful refining so as to greatly 
injure an originally good asphalt. It is evident, also, that an 
asphalt may be so far gone in the process of natural decay that, 
while it may serve to make what appears to be an excellent pave- 
ment, the life of such a pavement must be comparatively short. 
" Having thus shown how much depends upon the quality or 
nature of the bitumen in an asphalt rather than upon its mere 
percentage, it becomes important to know to what extent the 
chemist can distinguish this valuable quality, and so prevent dis- 
astrous mistakes in pavement work. It may be answered that a 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 285 

chemist who has made a special study of the subject can, by proper 
chemical analysis, aided by certain physical tests, point out what is 
probably good or worth trying in the case of new varieties, but it 
is impossible for' him to state for a certainty that a particular new 
variety will be fully equal in every essential respect to some stand- 
ard asphalt that has proved a success. Having learned by experi- 
ence the chemical and physical differences between good and bad 
samples of any particular asphalt, the chemist may thereafter 
afford valuable assistance in the use of that asphalt. 

" In view of the foregoing facts it would seem that the extensive 
use, for paving purposes, of any variety of asphalt that has not 
previously been proven a success by the test of actual trial for a 
sufficient length of time, under sufficiently adverse conditions, is 
in the nature of a rather hazardous experiment. 

"Trusting that the above answers and explanations will prove 
clear and satisfactory, we will add that they are given without 
prejudice and according to our best knowledge of the subject, 

" Yours respectfully, 
(Signed) "Chemist." 

Action of Water on Asphalt in the Laboratory. — It has fre- 
quently been claimed that there is a preference for one asphalt 
over another based upon the manner in which it behaves towards 
water when it is placed in contact with it in the laboratory. From 
data which will be given elsewhere x it appears that this method 
of examining them is not one the results of which are confirmed 
by practice. All asphalts are attacked by water under certain 
environments and some more than others under certain laboratory 
conditions. In practice, however, the results obtained in the 
laboratory are not confirmed if the asphalts are employed so as 
to bring out their most desirable qualities. 

Bearing in mind all these considerations it is not difficult to 
form a decided opinion as to the desirability of any native bitu- 
men for the uses to which it is put in the paving industry. 

1 See page 460. 



2S6 THE MODERN ASPHALT PAVEMENT. 

CONCLUSIONS. 

From the preceding data and discussion it is very evident 
that while many native bitumens may be denominated asphalt, 
from an industrial point of view, they possess no great uniformity 
in their physical and chemical properties and that some of 
them are far preferable to others for paving purposes. Some 
of them are extremely stable bitumens while others are more 
or less changeable on the application of heat. Some of them 
are hard, others are comparatively soft. Some evolve gas on 
heating, showing that they are unstable. Some lose on heating 
a considerable amount of light hydrocarbons, petrolenes, with 
corresponding hardening in the consistency of the material. Some 
asphalts are obtainable in unlimited amounts and of great uni- 
formity in composition. Others, while obtainable in large amounts, 
are very variable in their consistency, the character of no two 
shipments corresponding in this respect. Some asphalts, such as 
those which are obtained by collecting the exudation from maltha 
springs, are not only very variable in their character but, being 
still in a state of transformation from maltha to asphalt and, 
therefore, not in equilibrium, are unsatisfactory materials for use 
in the paving industry or require such great skill or judgment in 
their treatment as to make it difficult to construct good work 
with them. 

From the results of the author's experience with all the bitu- 
mens which have been used in the construction of asphalt pave- 
ments during the last eighteen years the conviction has been 
forced upon him that none of them, with the exception of gilsonite, 
which has recently proved itself under service tests to be a very 
desirable material, is as uniformly satisfactory as that obtained 
from the Trinidad pitch lake, and for the following reasons: 

1. The available supply is unlimited. 

2. The supply is of great uniformity, as appears from data 
given in the preceding pages. 

3. Asphalt cements prepared from Trinidad lake asphalt and 
stable flux are less liable to change in consistency when main- 
tained in a melted condition at high temperatures for any con- 
siderable length of time or on being tossed about in a mixer with 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 



287 



excessively hot sand, something that unfortunately happens too 
frequently, than one derived from any other form of bitumen. 

4. It is less susceptible to changes in consistency at extremes 
of temperature than any other native bitumen which is now used 
extensively in the construction of asphalt pavement. 

5. The relation of malthenes to asphaltenes is such that the 
proportion of flux which is necessary to produce an asphalt cement 
of normal consistency is not excessive. 

6. The mineral matter which it contains is of a nature most 
suitable to play the role of a filler and it is mixed by nature with 
the bitumen in a way that it is impossible to imitate by adding 
finely powdered mineral matter to a purer form of bitumen. 

Trinidad mixtures, when the mineral aggregate is properly 
graded and regulated, are not attacked by water to any greater 
extent on the street than mixtures made with other asphalts. In 
fact surface mixtures of Trinidad asphalt resist impact more sat' 
isfactorily after three months exposure to running water than 
those made with Bermudez asphalt, as shown by the following 
figures : 

IMPACT TESTS OF ASPHALT SURFACE MIXTURES. 



New York. 




Density 

Number of blows : 

Original material 

After 3 months' exposure to running water 

Water absorbed: 

Pounds per square yard 



16-14 
13 



Bermudez asphalt possesses the disadvantage that it is far from 
uniform in character, that the bitumens of which it consists are 
susceptible to volatilization at high temperature with a resulting 
hardening of the material, as for example when it is mixed with 



288 THE MODERN ASPHALT PAVEMENT. 

very hot sand ; that is to say, it does not form an asphalt cement 
which can be maintained at high temperatures or mixed with 
sand at high temperatures satisfactorily and for this reason cannot 
be used in cold weather, and because it is deficient, in com- 
parison with Trinidad asphalt, in mineral matter forming a natural 
filler. As has already been shown, surface mixtures made with 
Bermudez asphalt are more deteriorated by the continued action 
of water, as far as their resistance to impact is concerned, than 
those made with Trinidad asphalt. 

Maracaibo asphalt is not a normal asphaltic bitumen and 
possesses characteristics which throw a doubt upon its suitability 
for the preparation of a paving cement, which can only be removed 
by a study of its behavior after a long period of years in actual 
practice. 

Mexican asphalts are far from uniform and possess the same 
disadvantages that pertain to Bermudez asphalt. Their use would 
involve greater care and skill than any of the materials that have 
been mentioned. 

Cuban asphalts are very hard materials, approaching grahamite 
in composition, and must be fluxed with very large proportions 
of asphaltic oil. Their value as paving materials has never been 
satisfactorily demonstrated. 

The solid residuals from asphaltic or semi-asphaltic oils are 
far from uniform and are generally somewhat damaged or cracked 
in the course of their preparation. The closest scrutiny of these 
materials in the laboratory and the greatest skill in handling them 
is necessary to enable them to be used satisfactorily in the con- 
struction of asphalt surface mixture. 

Gilsonite has now been submitted to sufficient service test 
to show that as a paving cement it is equal in character to any 
asphalt in use for this purpose. A pavement was laid with it 
in 1903 on Missouri Avenue, Main to Delaware, Kansas City, 
Mo., under the author's direction, and it has proved entirely 
satisfactory. Since that time it has been used equally successfully 
to a large extent in other cities. Gilsonite may therefore be 
added to the list of those bitumens which are entirely suitable 
for paving purposes, if properly handled. This, of course, means 



COMPARISON OF VARIOUS NATIVE ASPHALTS. 289 

that the material shall be fluxed with an asphaltic oil, as a parafTme 
flux is entirely incompatible with the material. 

The preceding criticisms of the various asphalts which have been 
used in the construction of asphalt pavements lead at once to the 
conclusion that Trinidad lake asphalt or gilsonite is the best 
for this purpose. In the author's mind there is no reasonable 
doubt that this conclusion is correct. It is not intended, how- 
ever, to assert that satisfactory pavements cannot be constructed 
from the other asphalts, especially where the latter are not sub- 
jected to trying environment or a heavy traffic and where con- 
siderable skill is exercised in their use. It is asserted, however, 
that with Trinidad asphalt there is greater probability that a 
pavement constructed with it will be satisfactory, taking into 
account the fact that a greater or less lack of care is inevitable 
in preparing an asphalt surface mixture from any bitumen. Trini- 
dad asphalt will stand more abuse than any other ' material with 
which we are acquainted, and on this account is to be strongly 
recommended, as well as because less skill is required in handling it. 



SUMMARY. 

In this Chapter there is outlined the characteristics which make 
any solid native bitumen available and desirable for paving pur- 
poses. These characteristics are as follows: 

1. The quantity available. 

2. Its uniformity in character. 

3. Its stability in a melted condition at high temperatures. 

4. Its stability in consistency at the extremes of temperature 
which it meets in an asphalt pavement. 

5. The proportion of malthenes to asphaltenes which it con- 
tains. 

6. The proportion of flux which is required to make an asphalt 
cement. 

7. Mineral matter present and its character. 

It appears that Trinidad lake asphalt and gilsonite fulfil more 
of the necessary requirements than any other commercial supplies 
of native bitumen for the purpose of constructing asphalt pave- 
ments. 



290 THE MODERN ASPHALT PAVEMENT. 

It also appears that properly constructed surface mixtures 
made with Trinidad lake asphalt are no more acted upon by water 
than those made with other asphalts, and that the charge that 
they are acted upon to a greater extent is dependent purely upon 
laboratory experiments without regard to making the conditions 
under which they are carried on conform to tnose which are met 
with on the street. 



PART IV. 

TECHNOLOGY OF THE PAVING INDUSTRY. 



CHAPTER XV. 

REFINING OF SOLID BITUMENS. 

Asphalts which contain water as they occur in nature must 
be freed from it before they are in a condition to be used in the 
paving industry. The process of bringing this about is called 
refining. It really is nothing more than some method of drying the 
asphalt, in some cases removing the more volatile hydrocarbons, 
the loss of which, at a later period, from the asphalt cement 
would make the latter of unstable consistency, and skimming off 
any vegetable matter which may rise to the surface of the 
melted material. The process was originally called refining 
because, before the value of the fine mineral matter was un- 
derstood, much of this was separated out by subsidence 
from the melted bitumen and the resulting asphalt was actually 
refined, having been made purer or richer in bitumen. To-day 
the refining goes no further than the removal of such organic 
contamination as may rise to the surface of the melted asphalt 
after the water has been evaporated, and the volatile hydrocar- 
bons have gone off with the steam, and the thorough mixing of 
the residual mass to a condition of uniformity in composition, 
the mineral matter being maintained for this purpose in suspen- 

291 



292 THE MODERN ASPHALT PAVEMENT . 

sion, in the meanwhile, by agitation of the melted material in 
any convenient way. 

The drying process is conducted in two different ways. The 
material is filled into an iron tank or melting-kettle which is heated 
by a free fire, the bottom of the kettle being protected by an arch 
of brick; or a large rectangular tank is used, the interior of which 
is filled with gangs of pipe through which steam is conducted at 
such a pressure as to raise the asphalt to the same temperature 
that is produced over the free flame but without any danger of 
exceeding the highest temperature which the pressure of the 
steam will yield. Fig. 18. 1 In either case, since convection in 
such a viscous mass is very slow, agitation is carried on with either 
a current of air or steam, in the latter case the current not being 
admitted until the asphalt is melted and exceeds the boiling-point 
of water, this being necessary to prevent condensation and sub- 
sequent foaming. The temperature must, of course, be raised 
slowly at first to avoid foaming when the bitumen melts easily 
and the asphalt contains much water. When the temperature 
has been raised to a point where the material is thoroughly melted 
and steam is no longer given off the process is finished and the 
refined asphalt is ready to be drawn off. The details of this process 
are ones purely of economy, the object being to dry and get the 
asphalt into packages suitable for handling. Where the material 
is to be made into cement and used on the spot, the latter 
is unnecessary. The packages are usually old hydraulic cement 
barrels which before use are clayed on the inside by being re- 
volved in a bath of clay and water. The claying is done to make 
it possible to strip the staves from the asphalt more easily when 
preparing it at its destination to be made into cement and to do 
this with the loss of the least possible amount of asphalt adherent 
to the staves. 

In the fire refining method four or five days are required to 
complete the operation. In refining solid bitumens in this way 
danger is always incurred of overheating them, with the formation 
of coke and the cracking of the hydrocarbons. There is a certain 
formation of coke in all cases where a direct flame is in use and 

1 Page 405. 



RFFINING OF SOLID BITUMENS. 293 

that some asphalts are injured during the process is shown by the 
fact that the resulting bitumen is not entirely soluble in cold car- 
bon tetrachloride. To avoid such difficulties a very thorough 
mechanical or other form of agitation is absolutely essential. 

By the steam process the refining is completed in 24 hours 
or less without any danger of injury to the bitumen from over- 
heating. The agitation in this process is generally by means of 
dry steam. The use of steam results in the volatilization of a 
rather larger amount of lighter oils than occurs with air agitation 
and it may be possible, for this reason, that it could be replaced by 
air beneficially, although hot air has a decidedly strong effect upon 
native bitumens as has been shown in connection with the con- 
densed oils. 1 

From ten to twenty-five or more tons are refined at once, the 
larger amounts by the steam process, and the temperature reached 
is about 325° F. 

Almost all asphalts require refining but some other native 
bitumens which can be, and are, used to a small extent in the 
paving industry, are anhydrous and need no drying. Gilsonite and 
grahamite need no refining, being practically dry and pure bitu- 
mens. 

The Preparation of the Asphalt Cement. — Whatever solid 
bitumen and flux are selected for the purpose, their careful com- 
bination is necessary for the preparation of a satisfactory asphalt 
cement. The carefully weighed asphalt is melted and raised to 
a temperature of about 300° or 325° F., or if the material is taken 
on the immediate completion of refining, as happens where a 
refinery and paving plant are associated, it is carefully gauged. 
The flux, having preferably been heated with steam coils in the 
receptacle containing it to 150° to 200° F., is then slowly run into 
the melting-tank holding the asphalt, agitation with air or steam 
having been established, the air or steam being admitted through 
lines of pipe, perforated with frequent openings and which lie along 
the bottom of the tank. A satisfactory and sufficient agitation 
is most essential and steam has been found more suitable than 
air where its use is possible. It should, of course, be high pressure 

1 See page 273. 



294 THE MODERN ASPHALT PAVEMENT. 

steam and it should not be admitted to the melted asphalt until 
the latter is at such a temperature as to prevent condensation. 
Every provision should also be made that the steam be quite dry 
by blowing all condensed water out of the pipes carrying it. Neg- 
lect to do this will, otherwise, cause dangerous foaming. A check- 
valve should also be provided at a point above the surface of the 
melted asphalt to provide for the admission of air when the steam 
is shut off and prevent condensation and the production of a 
vacuum which will draw the melted asphalt cement back into 
the agitation pipes and clog them. Air agitation is simple and 
fairly satisfactory but the effect of blowing hydrocarbon oils 
with air results in hardening them and changing their consistency 
in a marked degree and on that account is undesirable. 

The agitation, of whatever kind, should be kept up until the 
solid bitumen and liquid flux are thoroughly mixed and in homo- 
geneous solution. The length of time required will depend on the 
force of the current of steam or air and the character and tem- 
perature of the melted materials. Under the most favorable 
circumstances three hours are requisite and with inferior agita- 
tion eight or more may be necessary. 

To the eye of the experienced yard foreman the point at which 
the combination is complete and the mixture homogeneous will 
be evident, but the material can be tested by pouring some of it 
into a pail of cold water and examining it on cooling Any oili- 
ness is a sign that more agitation is necessary. 

The asphalt cement having been found to be homogeneous 
the next step is the determination of the fact that the consistency 
is that which is desired. This can be arrived at in various ways 
of greater or less refinement. The ordinary, and always the pre- 
liminary test, is that of chewing a small piece of the cement 
cooled by pouring it into cold water. On putting the cement 
in the mouth and working it between the teeth it rapidly assumes 
the temperature of the mouth which is a very uniform one, that 
of the normal temperature of the body, 98.4° F. The amount 
of work that is done by the jaws upon the cement will readily 
show whether it is harder or softer than what experience has 
taught to be a proper consistency and it is not difficult for one 



REFINING OF SOLID BITUMENS. 295 

who makes this test daily to decide whether the asphalt in ques' 
tion is within four or five points of the consistency desired and 
registered by the more accurate penetration machine. In experi- 
enced hands it is questionable whether a more accurate test is 
absolutely necessary, except as a matter of record. 

A more refined test which is available for use by the yard fore- 
man at the plant is that known as a flow test which permits, ac- 
cording to a method described in Chapter XXVIII of comparing the 
relative flow, at temperatures above the softening point of the 
cement of the material to be tested with that of a standard of 
the desired consistency prepared in the laboratory. 

Where a definite determination is required for purposes of 
record one of the several penetration machines may be used, but 
these require careful manipulation and their use sometimes neces- 
sitates greater refinement than a yard foreman is capable of. 

Under any circumstance it is absolutely necessary that the 
consistency of the asphalt cement shall be so regulated that it 
will be entirely uniform for any one piece of work. What this con- 
sistency shall be will depend upon the character of the work which 
is being done and upon its environment, both as to traffic and 
climate. The variations in this respect will be discussed later. 

If the cement is to be held in a melted condition for any length 
of time agitation must be maintained, especially if it contains 
mineral matter. The purer native bitumens and residues from 
asphaltic petroleums require very little beyond that necessary to 
prevent any one portion remaining for any great length of time in 
contact with the source of heat, whether the walls of a tank heated 
by direct flame or the steam coils. All cements can be allowed to 
become solid and cold if they are thoroughly agitated again on 
remelting. On the other hand too powerful agitation is injurious 
as it volatilizes the lighter portions of the cement and hardens it. 
Continued agitation with air has a marked effect upon the charac- 
ter of all oils by the extraction of hydrogen and condensation of 
the hydrocarbons to a short rubbery solid such as the blown petro- 
leum now to be found on the market as an article of commerce, 
and which has been already described. The result of continued 
air agitation, therefore is to harden an asphalt in two ways, by 



296 THE MODERN ASPHALT PAVEMENT. 

the volatilization of the lighter oils and also by increasing their 
density by condensation of two molecules into one. Steam hardens 
a cement only by the volatilization of the lighter constituents. 
Steam is, therefore, probably preferable for the agitation of a fin- 
ished asphalt cement ; although air may be more desirable as a 
means of agitation during refining. 

The actual changes which take place with different fluxes and 
different asphalts will be shown further on. 

Character of Various Asphalt Cements. — The character of an 
asphalt cement depends upon that of the solid bitumen and of 
the flux from which it is prepared. 

Asphalt cements may be divided into several classes. 

1. Those composed of the standard solid native bitumens, such 
as Trinidad and Bermudez asphalts, and parafhne petroleum 
residuum. 

2. Those composed of the same asphalts and fluxes or residuums 
from asphaltic petroleums. 

3. Those made from the same asphalts and fluxes which are 
mixtures of asphaltic and paraffine oils. 

4. Those made from other solid native bitumens and asphaltic 
fluxes. 

5. Those composed of solid residual bitumens from asphaltic 
petroleum brought to a proper consistency with residuum of the 
same origin. 

6. Any of the first four classes with the addition of small 
amounts of the condensed or blown oil, or other forms of bitumen 
not constituting one of the main constituents of the cement. 

Asphalt Cements Composed of Trinidad or Bermudez and 
Similar Asphalts and Paraffine Petroleum Residuum. — Some years 
ago there was a popular prejudice against the use of paraffine 
petroleum residuum as a fluxing agent for asphalt. This was not 
founded on the results of any careful investigation or tangible 
evidence. It arose at first from a desire to find some excuse for 
the poor wearing quality of some carelessly constructed asphalt 
pavements and from the fact that the earlier surfaces were readily 
attacked by water where subjected to its action for any length of 
time. It was claimed: 

That a part of the residuum of paraffine petroleum is soluble in 



REFINING OF SOLID BITUMENS. 297 

water and that by the continued action of the latter on the oil in 
the asphalt cement , the cement is deteriorated. 

That on standing in a melted condition the petroleum oil rises 
to the top of the cement and can be " skimmed off like cream." 

That the bitumen of Trinidad and other asphalts are not com- 
pletely soluble in paraffine residuum but are only mechanically 
mixed. 

The fallacies in two of these claims are readily shown. 

That the first is false is shown by the fact that distilled water 
which has been allowed to stand in a glass-stoppered bottle in 
contact with standard paraffine residuum for four years is as 
bright and clean as when first put there and contains nothing in 
solution. 1 

The second is equally wrong since a tank of asphalt cement 
maintained one week at a temperature of 300° F. ; without agita- 
tion, on cooling, was not to the slightest degree oily or greasy on 
the surface, which would be the case if any oil had separated like 
cream. 

The proposition that the bitumen of Trinidad and other asphalts 
is not completely soluble in standard paraffine petroleum residuum 
can be equally well disproved and it can be shown that asphaltic 
bitumens are as soluble in paraffine residuum as in the asphaltic 
oils of California. The results of some experiments in this direc- 
tion by the author were presented in articles in " Municipal 
Engineering " for June, July and August, 1897, and for June, 1899. 
The experiments and conclusions arrived at and presented in the 
latter article were, in the main, as follows: 

"Three asphalt cements, prepared with great care and uni- 
formity, as appears from the results of duplicate analyses of the 
original material, were placed several inches deep in glass tubes 
8 inches long and J of an inch in diameter and maintained at a 
temperature of 325° F. for three days, being centrifugaled at that 
temperature several times to assist any separation that might take 

1 Messrs. Whipple and Jackson in a paper read before the Brooklyn En- 
gineers Club and published in the Engineering News for March 22, 1900, have 
shown that petroleum residuum is affected less by water than any bitumin- 
ous substance that they examined. 



298 



THE MODERN ASPHALT PAVEMENT. 



"RESULTS OF CENTRIFUGAL ACTION ON VARIOUS ASPHALT 

CEMENTS. 

"100 lbs. Trinidad + 20 lbs. of paraffine residuum. 





Original 

Cement. 

Duplicates. 


Top 

45 Per Cent. 
Duplicates. 


Bottom 
45 1 er Cent. 
Duplicates. 


Sedi- 
ment, 
10 Per 
Cent 


lt Bitumen soluble in chloroform. . 








27.6 


Bitumen soluble in CS 2 


63.4 63.5 

48.6 48.7 

76.6 76.6 
23.4 23.4 

30.3 

6.3 

55° 


69.9 70.1 
53.4 53.4 

76.3 76.2 
23.7 23.8 

23.9 

6.2 

49° 


68.5 68.7 
52.7 52.9 

76.9 77.0 
23.1 23.0 

25.1 

6.4 

51° 


26 8 


Bitumen soluble in 88° naphtha. . 
Per cent of total bitumen thus sol- 
uble 


22.3 
83 2 


Per cent of total bitumen insoluble 
Mineral matter. 


16.8 
65.5 




5.4 


» 
Penetration 






100 lbs. Trinidad + 27 lbs. California 'G' grade flux. 



" Bitumen soluble in chloroform , 
Bitumen soluble in CS 9 



Bitumen soluble in 88° naphtha . . . 
Per cent of total bitumen thus sol- 
uble 

Per cent of total bitumen insoluble 



Mineral matter. 

Difference 

Penetration. . . . 



64.7 64.8 
51.1 51.3 

79.0 79.2 
21.0 20.8 

28.9 

6.4 

46° 



71.6 71.9 

55.7 56. C 

77.8 77.9 
22.2 22.1 

22.9 

5.5 

47° 



70.2 70.4 
55.1 55.4 

78.5 78.7 
21.5 21.3 

23.0 

6.8 

50° 



27.3 
26.8 
22.5 

84.0 
16.0 

65.8 

7.4 





"100 lbs. Bermudez + 18 lbs. of paraffine residuum. 



"Bitumen soluble in chloroform. . 

Bitumen soluble in CS 2 

Bitumen soluble in 88° naphtha. . 
Per cent of bitumen thus soluble . . 
Per cent of total bitumen insoluble 



92.6 92.8,96.2 96.4 

73.1 73.2:74.5 74.7 

78.9 78.9,77.4 77.5 

21.1 21.122.6 22.5 



Mineral matter. 

Difference 

Penetration at 78° F. 



3.2 3.3 

4.2 3.9 
60° 



1.9 
1.9 

56° 







95.2 
73.6 
77.3 
22.7 


95.4 

73.8 
77.4 
22.6 


2.2 


2 


6 


55° 



67.5 
66.8 
53.9 
80 7 
19.3 

15.0 

8.2 




REFINING OF SOLID BITUMENS. 299 

place. On cooling the asphalt was divided into three parts; an 
upper, 45 per cent; a lower, 45 per cent; and the bottom, 10 per 
cent, of sediment. The consistency and composition of these por- 
tions were then determined by the most careful methods, extract- 
ing with naphtha and carbon disulphide, filtering on a Gooch cru- 
cible and burning the bitumen solution for any inorganic correction. 
The results were obtained in duplicate, except in the case of the 
sediment. Their agreement is confirmatory of their accuracy. See 
results tabulated on page 298. 

" These results show that there is no difference in the char- 
acter of the bitumen in the cement made from Trinidad asphalt 
and residuum in the two portions of cement above the residue, 
after heating and subsidation, from that of the original material. 
With California oil and Bermudez asphalt there is a slight loss of 
oil in the upper portions and consequent small reduction in the 
percentage of naphtha soluble bitumen. In the sediments the pro- 
portion of naphtha soluble to total bitumen has increased in all 
three cements. The fact that something in the cement more solu- 
ble in naphtha and heavier than the ordinary constituents has been 
thrown down, is peculiar." 

What this is it is impossible to say at present, but it appears 
from a paper by R. P. Van Calcar, which has recently appeared in 
the Recueil des Travaux Chimiques des Pays-Bas, 1 that where solu- 
tions of various salts in water were subjected to a centrifugal force 
400 times that of gravity they became more concentrated at the 
periphery after a few hours, contrary to the preconceived ideas that 
the molecules in a true solution were unaffected by gravity, and 
hence were in a different state from those in colloidal solutions. 
As a consequence of Van Calcar's conclusions the results obtained 
with the asphalt cement are not unexpected. 

"As a whole the results seem to the writer to refute the state- 
ments which have T^een made in regard to residuum and to show 
that 90 per cent of the asphalt cement made of Trinidad lake 
asphalt and residuum was unchanged to any perceptible degree 
after the severe treatment it had been subjected to by standing 
and centrifugaling at a high temperature, while any changes that 
1 Science, 1904, August 19, 20, 250. 



300 



THE MODERN ASPHALT PAVEMENT. 



took place in the sediment were found as well in cements made 
with the California residuum or so-called asphaltic flux." 

As a matter of fact there is no evidence to show that there is 
any essential difference between the California fluxes and parafnne 
residuums in their power of dissolving the bitumen of Trinidad and 
Bermudez asphalts, or that the latter is not a satisfactory flux, 
on this account, for making asphalt cements with these asphalts. 
The successful use of it in many pavements laid twenty years ago, 
which are now in perfect repair, is the best evidence that it is 
satisfactory. 

Amount of Residuum Necessary in Making An Asphalt Ce- 
ment. — The amount of parafnne residuum oil which it is necessary 
to use per 100 pounds of Trinidad or Bermudez asphalt to make a 
cement of satisfactory consistency depends on the character of 
this flux. It may be very variable, but with a standard material 
should not vary more than 4 pounds per hundred of the asphalt. 
With some less carefully prepared residuums the difference may be 
6 pounds. For example the oil in use by one company in 1899 
and by another in 1898 had the following characteristics : 



Residuum 


Light 

.9197 
22 7° 
330° F. 
17.3 

16 
14 


Heavy 

.9331 
20.5° 


Specific gravity, 78° F./78° F., orig. mat., dry 
Beaume 


Flashes, ° F 


442° F. 


Loss, 400° F., 7 hours 


3.8% 
22 


Pounds per 100 of asphalt to make asphalt 
cement of 60° penetration : 

Trinidad lake 


Bermudez 1899 


23 







Much less of the lighter oil would produce the same softening 
effect as the larger quantity of the heavier residuum. It becomes 
a question then to determine as far as possible which is the most 
desirable cement and the only evidence that is available are the 
results of an examination of the two cements as to the change in 
their consistency at such extremes of temperature as are common 
in pavements and as to their change in penetration on being main- 



REFINING OF SOLID BITUMENS. 



301 



tained in a melted condition for some time, 
directions furnish the following information: 



Experiments in these 



COMPARISON OF CONSISTENCY OF ASPHALT CEMENTS AT DIF- 
FERENT TEMPERATURES WHEN MADE WITH DIFFERENT 
FLUXES. 



J* sphalt. 


Residuum. 


Pounds 
per 100 

of Asphalt. 


Penetration at 




45° F. 


78° F. 


100° F. 


Bermudez 

Trinidad 

<< 


Light 
Heavy 
Light 
Heavy 


14 
23 

16 

22 


30° 
32 
29 
29 


60° 
60 
65 
63 


105° 
125 
120 
115 



PENETRATION AND LOSS AFTER HEATING TO 300° FAHR. 







Penetration at 78° F. 


Loss. 






Orig- 
inal. 


After 
Heating 
4 Hours 


After 
Heating 
6 Hours 


1st 
2 Hours 


2d 
2 Hours 


3d 
2 Hours 


Total. 


Bermudez. . . 
<< 

Trinidad. . . . 

a 


Light 
Heavy 
Light 
Heavy 


60° 
60 

65 
63 


36° 

50 
35 
40 


30° 
45 
30 
38 


1.36% 

.50 
1.56 

.98 


.79% 
.40 
.75 
.34 


•71% 
.30 
.58 
.33 


2.86% 
1.20 
2.89 
1.65 



At temperatures between 78° and 45° F. there is no great 
difference in the penetration of cements made with heavy and 
light residuum. At higher temperatures there is a considerable 
but not constant difference. In the case of Bermudez cements, 
that made with the heavy oil is softer at 100° because of the 
greater softening effect of the larger amount of flux, 23 pounds, 
as compared to 14 of the lighter oil, while with the harder Trinidad 
the reverse is the case. As will be seen later, a flux which is so 
dense that an excess of it is required to produce a cement of normal 
consistency at ordinary temperatures may make a cement more 
susceptible to high temperatures than a lighter or less dense one. 

As to the permanency of the two classes of cement, however 
the figures show that on maintaining it in a melted condition, 



S02 THE MODERN ASPHALT PAVEMENT. 

and of course on mixing with hot sand, there is a much larger loss 
of oil and a greater hardening of the cement fluxed with light than 
with heavy residuum. For this reason alone cements made with 
the heavier oil seem, up to a certain point, decidedly preferable to 
those made with the lighter forms in use. Determinations of the 
consistency of the bitumen in old surfaces laid with cements made 
with light residuum as compared with others holding heavy oil 
confirm this. Surfaces in Omaha were laid in 1890 in part with a 
light, so-called summer o'.l, and in part with a heavy one. The 
consistency of the bitumen in these different surfaces when laid 
and again on extraction was as follows: 



Flux in Cement. 


Original Pen. 


Pen. 1899. 


Loss. 


Light 
Heavy 


67° 

50° 


35° 

30° 


32° 

20° 



It seems that the cement made with the very light oil has 
hardened, either in the mixer or by age, to a much greater extent 
than the other. 

Many good pavements have been made with the lighter fluxes, 
however, and it would be unfair to condemn them entirely, or to 
say that they are necessarily the cause of defects in asphalt sur- 
faces, but it seems plain that the heavier oil is in general the more 
satisfactory although more of it must be used. 

In the light of the previous results no valid objection can be 
raised and maintained against the use of a suitable paraffine petro- 
leum residue as a flux for Trinided lake and Bermudez bitumens 
in the preparation of an asphalt cement, and this is not surprising 
when it is considered that many million yards of satisfactory 
pavement have been laid with such a cement. 

Paraffine residuums are to be found on the market, and this 
was the case very frequently in the early days of the industry, which 
are, owing to the manner in which they have been prepared, quite 
unsuitable for use, but this has no bearing on the question of the 
availability of standard material. 

For fluxing Trinidad land asphalt and others of a hard nature 
paraffine residuum is not suitable because of the deficiency of 



REFINING OF SOLID BITUMENS. 303 

lighter malthenes in these asphalts, the lack of which is not made 
up by the hydrocarbons of such a residuum. 

Asphalt Cements Composed of Trinidad or Bermudez and Simi- 
lar Asphalts and Flux or Residuum from Asphaltic Petroleums. — 

Trinidad, Bermudez, and other similar asphalts can be satisfactorily 
fluxed with the asphaltic residuums which are prepared in the 
East from Texas oil and are now on the market. The char- 
acter of this residuum has already been described. It is a 
most desirable material and can be used in about the same pro- 
portions and in exactly the same way as the paraffine petroleum 
residuum. It should not, however, be so dense as to necessitate 
the use of excessive amounts of it, since under these conditions, 
as was shown to be the case with paraffine residuum, the resulting 
asphalt cement will be too susceptible to high temperatures. The 
density should be such that not more than 22 pounds of oil per 
100 of refined Trinidad or of Bermudez asphalt shall be required 
to produce a cement of 65° penetration on the Bowen machine. 
Such an oil will have a density of .95. The heavier residuum of 
a density of .97, also found on the market, is not satisfactory, 
although this flux has its use with certain other native bitumens. 

Comparing the general characteristics and stability of the 
two forms of residuum it has been found and confirmed by prac- 
tical experience that there is probably a slight preference in favor 
of a not too dense asphaltic flux, but this difference is not sufficiently 
great to make it obligatory to use the latter except in work of the 
very highest character on streets which carry very heavy traffic 
and where it is certain that the character of the asphaltic will 
be as uniform and satisfactory as that of the paraffine flux, and 
unfortunately this is not always the case. The greatest care is 
necessary in its preparation, as any overheating or cracking in the 
latter will result in the presence of light oils which volatilize readily 
and cause a rapid change in the consistency of the cement, while 
maintaining it in a melted condition or during the time that the 
cement is being tossed about in the mixer in contact with hot 
sand during the preparation of surface mixture. It is possible, 
therefore, that in comparison with an asphaltic flux of inferior 
grade a paraffine residuum may be preferable. 



304 THE MODERN ASPHALT PAVEMENT. 

Combinations of Trinidad, Bermudez, and similar asphalts with 
the heavy California flux known as No. 2 or G grade are not satis- 
factory, since the proportion of such a flux to the asphalt in order 
to produce a cement of proper consistency is so large, being in the 
neighborhood of 60 pounds of flux to 100 of Trinidad asphalt, that 
the resulting material is excessively susceptible to high tempera- 
tures. Such combinations are, therefore, rarely used. Where 
the solid asphalt is one that has been much hardened by age or 
exposure, as in the case of that from La Patera in California, a 
supply of which is no longer on the market, the mine being ex- 
hausted, the use of a heavy California flux or a very dense Texas 
residuum is imperative, at least as a preliminary fluxing material, 
to supply the lack of denser malthenes in the asphalt. If a certain 
amount of this flux is used, however, the remainder can be of a 
lighter form, and probably preferably so. Asphalts of this descrip- 
tion are not at present of commercial interest, with the exception, 
perhaps, of that obtained in Cuba from the Bejucal mine. 

Asphalt cements have sometimes been made from the solid 
native bitumens, including the asphalts, and the natural malthas. 
Pavements constructed with asphalt cements made in this way 
have proved, however, to be unsatisfactory. Some experiments 
were conducted some years ago by the writer to determine why 
such asphalt cements were not satisfactory. 

In the laboratory it was found that the solubility of the bitu- 
mens of Trinidad and Bermudez asphalts was as great in the 
ordinary malthas as in the residuums from paraffine and asphaltic 
petroleums. There was no preference in this respect. When, 
however, the permanence of consistency of malthas when exposed 
to heat was compared with that of residuums, there was found 
originally to be a great deficiency in that of the malthas. 

Residuum such as is at present in use has already been shown 
to volatilize but a small amount when heated in an open dish 
in a bath kept at 400° F. for 7 hours, and to remain of the same, 
or very nearly the same, consistency after as it was before heating. 
The desirable features of a carefully prepared residuum as a soften- 
ing agent are not lost on continued heating, nor is there sufficient 



REFINING OF SOLID BITUMENS. 305 

oil volatilized at the high temperatures at which asphalt cement 
is maintained in a melted condition, with agitation for consider- 
able periods of time in large masses, to change the consistency 
to any marked degree. As an example, a Trinidad lake asphalt 
cement made on February 29, 1896, by mixing 100,000 pounds 
of refined asphalt with 20,000 pounds of residuum had a pene- 
tration of 55°. It was held over a very low fire in a melted con- 
dition for 48 hours and then had changed in consistency so little 
as to penetrate 49°. After 73 hours melting the penetration was 
46°. This is an extremely small change for such a considerable 
length of time. 

Asphalt cements made with the native malthas behave quite 
differently. On heating for any considerable time they are con- 
verted into hard and glassy pitches by volatilization of oil, and, 
perhaps, by condensation of its hydrocarbon constituents. Such 
material is unstable and cannot form a cement which can be 
maintained at a uniform consistency. 

On Saturday, February 29, 1896, in the early morning, 500 
pounds of Bakersfield maltha was added to 2000 pounds of refined 
Trinidad asphalt, or at the rate of 25 pounds to the 100. After 
agitation the resulting asphalt cement penetrated 55°. It was 
allowed to stand with a low fire until the following Monday morn- 
ing, March 2. The penetration had then fallen to 25°. On stand- 
ing another 24 hours the penetration was found to be 22°. 270 
pounds of additional maltha was then added, corresponding to 
13.5 pounds per 100, whi^h, after agitation, raised the penetration 
to 54°. After 4 hours of heating and agitation a sample was 
taken and found to penetrate but 35°. 

It appears from this experiment that the light native Cali- 
fornia malthas are not suitable for the preparation of an unchange- 
able cement. Why this is so can be seen in the results of an exam- 
ination of the maltha in the laboratory. While it is thick enough 
to require 5 pounds more of it to every 100 pounds of Trinidad 
refined asphalt to make a cement of the same consistency that 
is obtained with residuum, it loses on heating for 7 hours to 400° F. 
20.3 per cent. This light oil is, of course, volatilized, in the same 



306 THE MODERN ASPHALT PAVEMENT, 

way, though more slowly, from the asphalt cement made with 
the maltha, and the loss causes the rapid fall in penetration and 
hardening of the cement. 

An experiment with one of the asphaltic oils extracted from the 
abundant supply of asphaltic sandstone rock in Texas resulted 
similarly. The asphaltic oil, or maltha, as received was heated for 
some time at a low temperature to drive off any water and very 
volatile oil. A cement was then made of Trinidad asphalt and the 
maltha in the proportion of 100 to 80, which had a penetration of 
65°. This cement was then maintained for 9 hours at a tempera- 
ture of 325° F., when it was found to have hardened so much as to 
penetrate but 24°. 

Of course satisfactory surface mixtures for paving cannot be 
made with such changeable material, and this is the reason that 
much of the earlier work done with California asphalt was a fail- 
ure. 

In fact, slight reflection shows that for a fluxing agent for 
softening hard asphalt a substance is needed which does not 
change its consistency after prolonged heating, and not 
another, though perhaps softer asphalt, which gradually 
becomes converted into a hard asphalt under the influence 
of heat. 

Asphalt Cements Composed of other Solid Native Bitumens 
than Ordinary Asphalts and Asphaltic Fluxes. — Entirely satis- 
factory cements for use in the paving industry have been made 
from some of the other native bitumens, especially Gilsonite, 
by fluxing them with an asphaltic oil. For this purpose about 
equal parts of the Gilsonite and flux are necessary. The resulting 
cement contains bitumen in the form of the classes known as 
malthenes and asphaltenes in normal proportions, about the 
same as in Trinidad and Bermudez asphalt cements, as will appear 
from data on page 308. On this account, such cements may be 
regarded as entirely normal in character, and the fact that they 
contain a large proportion of flux is not open to comment, espe- 
cially as the hard bitumen and the oils combine homogeneously 
and no free flux is found in the cement. 



REFINING OF SOLID BITUMENS. 307 

Asphalt Cements Composed of Solid Residual Bitumens from 
Asphaltic Petroleum Brought to a Proper Consistency with 
Residuum of the Same Origin. — From the asphaltic petroleums, 
such as those found in California and Texas, residual pitches or 
solid bitumens are prepared by distillation, and the charac- 
teristics of these solid bitumens have been already described. 
Asphalt cements can be prepared for paving purposes from these 
residual pitches by bringing them to a proper consistency with 
a residuum or flux made from the same petroleum. These cements 
have been used with some success and also with many resulting 
failures. They are very susceptible to temperature changes, 
which necessitates the use of a very carefully graded mineral 
matter with plenty of filler and the greatest skill in handling 
them in order that they may not harden while being mixed with 
hot sand or reach the street at such a degree of softness that they 
mark up very rapidly under hot summer suns. 

Cements of this description have been used to a very consider- 
able extent on the Pacific Coast, and they are quite suitable for 
the climate of Southern California. In Washington and Oregon 
some difficulties have been met with where they have been employed. 

Asphalt Cements of Any of the Previous Classes to which 
Amendments of Residual Pitches or Blown Oils Have Been Added. — 
Excellent asphalt cements have been prepared for paving purposes 
to which additions, not exceeding 10 per cent in amount, of con- 
densed or blown oils, such as Pittsburg flux, Ventura flux, or blown 
Beaumont oil have been made. While tne materials constituting 
these additions are in themselves unsuitable for paving purposes, 
they seem in some instances to modify the properties of native 
bitumen in such a way as to improve them, although in a manner 
that cannot be described. Such cements are not to be objected 
to, since they have been shown by experience to give satisfactory 
results. 

Characteristics of Asphalt Cement. — It is of interest to note 
the characteristics of asphalt cement prepared from various bitu- 
mens with various proportions of fluxes, especially as to the rela- 
tive proportions of the malthenes" and asphaltenes which they 



308 



THE MODERN ASPHALT PAVEMENT. 



contain. Some data in regard to this are given in the following 
table : 



Asphalt. 


Flux. 


Proportions. 


a 

4} 

o 
PQ 

a 

Ph 


a? 
o 
>> 

a 

1 

n 


M 

0J 

"el 
3 

u 

a> 
a 


o 

s 




00 
00 

S 


"3 
o 
H 

■♦» 
a 

V 

O 
u 
a> 

P^ 


i 

1 


Trin. Lake . 


Texas 

asphal- 

tic 


100-19.0 
100-25.0 
100-33.3 


40 
60 
80 


64.2 
67.6 
70.0 


31.0 

28.3 
25.9 


4.8 
4.1 
4.1 


46.7 
50.2 
52.2 


72.7 
74.3 
74.6 


8.3 
8.2 
7.6 


Trin. Lake . 


Paraf- 
fine 


100-19.5 
100-23.5 
100-26.6 


40 
60 

80 


64.7 
66.1 
67.5 


30.5 

29.2 
27.7 


4.8 
4.7 
4.8 


46.0 
47.2 
48.6 


71.1 
72.6 
72.0 


8.9 
8.8 
8.1 


Trin. Land. 


Paraf- 
fine 


100-17.6 
100-25.0 
100-28.2 


40 
60 
80 


63.1 
64.3 
65.5 


30.9 
29.6 
28.8 


6.0 
6.1 
5.7 


44.3 
47.3 
49.0 


72.0 
73.5 
74.8 


9.2 
9.8 
9.0 


Berm. Lake. 


Texas 

asphal- 
tic 


100- 5.3 
100-14.9 
100-22.0 


40 
60 
80 


94.8 
95.2 
95.0 


2.4 
2.4 
2.1 


2.8 
2.4 
2.9 


69.0 
71.6 
72.2 


72.8 
75.1 
76.0 


13.0 
12.1 
11.6 


Berm. Lake. 


Paraf- 
fine 


100- 5.3 
100-14.9 
100-22.0 


40 
60 
80 


94.2 
95.5 
95.4 


2.2 
2.0 
2.2 


3.6 
2.5 

2.4 


68.0 
71.0 
71.3 


72.2 
74.3 
74.7 


12.7 
12.4 
12.2 


Gilsonite . . . 


Texas 

asphal- 

tic 


100-85.2 
100-96 . 1 


60 
80 


99.7 
99.8 


.2 
.1 


.1 
.1 


76.3 

76.8 


77.1 
77.6 


8.1 

7.7 


D grade, Cal. 


G grade 


100-12.4 


80 


99.7 


.2 


.1 


70.8 


71.5 


16.0 


Texas resid- 
ual pitch 


Texas 

asphal- 
tic 


100-20.4 
100-25.0 
100-33.3 


40 
60 
80 


98.6 
98.9 
98.8 


.2 
.2 
.1 


1.2 

.9 
1.1 


70.5 
71.9 

73.8 


71.5 

72.7 
74.7 


19.1 
18.3 
17.2 


Cuban Beju- 
cal 


Texas 

asphal- 

tic 


100-49.0 
100-50.0 
100-55.0 


40 
60 
80 


68.3 
70.0 
76.0 


26.1 
23.5 
18.1 


5.6 
6.5 
5.9 


48.8 
50.7 
56.0 


71.4 
72.4 
73.7 


11.9 
11.1 
11.0 


Grahamite. . 


Texas 

asphal- 

tic 


100-150.0 
100-203.0 
100-233.3 


40 
60 
80 


99.5 
99.5 
99.5 


.1 
.1 
.1 


.4 
.4 
.4 


63.3 
70.4 
71.3 


63.6 
70.7 
71.6 


9.8 

8.4 
8.1 



Physical Properties of Asphalt Cement. — The character of 
a sheet asphalt surface of ordinary type will depend very largely 
on the properties of the cementing material which binds the mineral 
aggregate together, even if the latter is of the most approved 



REFINING OF SOLID BITUMENS. 309 

grading and consequent stability. When the latter is not careially 
arranged the physical properties of the asphalt cement will have 
an even greater influence on the behavior of the asphalt surface, 
more particularly under great extremes of temperature. It is 
important, therefore, to examine the properties of asphalt cements 
prepared from different solid native bitumens and softened with 
various fluxes. The properties which are of the greatest impor- 
tance have been generally accepted to be their greater or smaller 
susceptibility to changes in consistency at the extreme temperatures 
which they meet under different climatic conditions and to their 
variable ductility. 

The fact that asphalt cements vary in consistency, with change 
of temperature, means that at certain temperatures they are very 
viscous liquids and at low temperatures slightly viscous solids, the 
transition from one state to another being very gradual, although 
under modern theories of physical chemistry substances which are 
not crystalline can hardly be regarded as being solids. The slow 
flow of crude Trinidad asphalt, where large heaps of it are stored, 
is a well-known occurrence and corresponds very closely to that 
of the glacial flow of ice. The flow of an asphalt cement con- 
taining a very considerable proportion of flux is, of course, much 
more rapid. Mr. A. W. Dow 1 has shown that when cubes of asphalt 
cement are placed over a hole in a board at temperatures of 26° F., 
75° F. and 140° F., the movement of the material into the hole 
was visible in 1 hour at 140° F., in a longer time at 75° F., and in 
I week at the lowest temperature. The fact that an asphalt cement 
will flow at this low temperature is of great importance in connec- 
tion with the behavior of asphalt surface on the street in the winter 
months. Unless there is some ductility to allow for the contraction 
in the mass of the mineral aggregate all asphalt surfaces would 
crack at such a season. That they do not do so in all cases is to 
be attributed to this and to the fact that a suitable asphalt cement 
possesses such a consistency and lack of susceptibility to change 
m this respect between the lowest and the highest temperature 
to which it is exposed as to prevent it. Cracking frequently does 

1 Municipal Engineering, 1898, 15, 364. 



310 THE MODERN ASPHALT PAVEMENT. 

take place in asphalt pavements from the lack of such qualities 
in the asphalt cement of which they are composed or from the 
absence of a sufficient amount of it as will appear in the discussion 
in later pages on the defects in asphalt pavements, 1 but is oftener 
due to the hardness of a cement rather than to its lack of ductility 
as experiments have shown that some asphalt cements, if suffi- 
ciently soft, although very short, may be sufficiently ductile to 
meet the demands made upon them at low temperature. 

Experiments have shown that the ductility of an asphalt 
cement is proportionate to the amount of flux which it contains 
rather than to the character of the same and as the result of a 
very extended investigation, the results of which are too lengthy 
and numerous to introduce here, it has been made evident that 
too much dependence cannot be placed upon this characteristic 
in forming an opinion as to the availability of an asphalt for paving 
purposes. 

The susceptibility of asphalt cements to changes in consistency 
with change in the temperature of its environment can be shown 
in several ways, most conveniently by determining the consistency 
at different temperatures with one of the various penetration 
machines in use for this purpose, by the relative elongation of 
cylinders of different cements under tension at different tempera- 
tures or, in the case of high temperatures, by the length of flow 
of small cylinders of cement on a corrugated brass plate in the 
manner described in Chapter XXVIII. If asphalt cements are 
prepared from different asphalts and fluxes of such a consistency 
that they all have the same penetration at the normal tempera- 
ture, 78° F., and are then again penetrated at extremely low 
and high temperatures the relative changes in the consistency 
can then be determined, as has been already shown. 2 

In the following table are presented the results of the deter- 
mination of the consistency of the asphalt cement made from 
various asphalts with fluxes of different character at 41° F. and 
100° F. all the cements having the same consistency at 78° F. 

Although the results speak for themselves it may be we 11 to 

1 See page 480-2. 2 See page 301. 



REFINING OF SOLID BITUMENS. 
THE MODERN ASPHALT PAVEMENT. 



311 



Asphalt. 


Flux. 


Parts 
Flux to 

100 of 
Asphalt. 


Pen. 
Bowen, 

78° F. 


Penetrometer. 


41° F. 1 


78°F.i 


100° F.i 


Trinidad Lake .... 
(i n 

n it 

Bermudez 

1 1 

it 

Durango 


Heavy 

Extra Heavy . . . 
Paraffine 

Heavy 

Extra Heavy . . . 
Paraffine 

None 


25 

34 
22 

17.5 

24 

15 

127 
170 
122 

270 

51 


65 
65 
65 

65 
65 
65 

65 

65 
65 
65 

65 

65 


3 
2 
5 

5 

3 
3 

3 

5 
5 

7 

6 
5 


41 

42 
32 

44 
40 
39 

43 

34 
37 
30 

28 

22 


97 

113 

91 

100 
109 
108 

98 


Gilsonite 


Heavy . . 


63 


1 1 

K 


Extra Heavy . . . 
Paraffine 

Extra Heavy . . . 

Heavy 


82 
48 


Grahamite 

Cuban Bejucal 


35 
37 







1 41° F. = 200 grams, 5 seconds; 78° F. = 100 grams, 5 seconds; 100° F.= 
50 grams, 5 seconds. 

call attention to some of the facts that are brought out by them. 
Among the Trinidad cements that made with extra heavy oil, 
and consequently requiring the largest proportion of flux, is 
much more susceptible to high temperatures, having a penetra- 
tion at 100° F. of 113°, while that made with the paraffine oil, 
of which only 22 pounds per 100 was employed, has a penetra- 
tion of only 91°, while all the Trinidad cements had practically 
the same penetration at 41° F. 

Asphalt cements made with gilsonite and grahamite are much 
less susceptible to changes in consistency at extreme tempera- 
tures. At 41° F. cements made from these materials, although 
having the same penetration as the Trinidad, Bermudez, and 
California cements at 78° F., are much less hard and in the same 
way are softer to a less degree at higher temperatures. This 
would show that such cements would be more satisfactory for use 
in the paving industry where extremes of temperature are to be 
met than those composed of true asphalts. 



312 THE MODERN ASPHALT PAVEMENT. 

SUMMARY. 

In the preceding chapter the technology of the paving indus- 
try has been discussed in detail from the refining of the native 
bitumen to the preparation of the asphalt cement, together with 
a study of the character of the various asphalt cements made 
from different solid bitumens and with different fluxes. This 
chapter in its detail will interest principally the asphalt expert, 
the engineer, and the specialist. 



CHAPTER XVI. 
SURFACE MIXTURES. 

The surface mixtures of the early days of the asphalt paving 
industry consisted, as they do to-day, of asphalt cement, ground 
limestone, and sand; but even in 1893 very little attempt was made 
to specify fhe character of these consituents or to determine what 
roles they play in the finished pavement. The asphalt cement was 
at one time soft, at another hard, at one time too small in amount 
and again too large, but oftener too small; the ground limestone 
was expected in 1884 to be only so fine that 16 per cent should be 
an impalpable fine powder and all should pass a No. 26 mesh, 
hardly what would be considered a dust to-day, and at times it 
was held to be doubtful if there were any necessity for the use 
of dust at all. The sand was sometimes coarse and sometimes 
fine, depending on the most available local supplies, and only in 
the later years were two kinds mixed and that without much 
reasoning. 

In 1884 it was specified that the sand in use in Washington should 
all pass a 20-mesh sieve and none of it an 80. x 

Surfaces with coarse sand and much cement marked or pushed 
and then the bitumen was reduced; with fine sand and low bitumen 
they cracked and the other extreme was again sought. Every- 
thing was done by rule of thumb and without reason. To this 
state of affairs much, but not all, of the cracking, displacement, 
and defects in pavements laid in the early nineties was due. The 
average consistency of the cement was the same for years and was 

1 Annual Report of the Operations of the Engineer Dept., District of 
Columbia, for the year ending June 30, 1884, 101. 

313 



314 



THE MODERN ASPHALT PAVEMENT. 



too hard in most cases because the defective mineral aggregate 
would not permit the use of a softer one. The limestone dust was 
most of it sand and in consequence the amount of filler in the mix- 
ture was very deficient. But, worst of all, the sand grading was 
arranged by chance. Specimens of old surfaces were collected 
in 1894 and studied by the author at the request of the President 
of the Barber Asphalt Paving Company as being representative 
of the best work of the company up to that time, although they, 
on this account, hardly illustrate the average pavement of that day. 
They were analyzed in Washington and showed the following 
variations in their mineral aggregate, filler, and bitumen. Among 
these variations those in the sand grading are most striking. 

AVERAGE COMPOSITION OF SURFACES FROM VARIOUS CITIES, 
LAID BEFORE 1894, ARRANGED ACCORDING TO THE PER- 
CENTAGES OF 100- AND 80-MESH SAND THEY CONTAIN. 



City. 



Bitumen. 



Mineral Aggregate Passing Mesh 



200. 



100 and 80 



50 and 40 



30,20, and 
10. 



Total. 



Washington 

Louisville 

Newark 

St. Louis 

Youngstown 

New Orleans 

New York 

Scranton. 

Boston 

Kansas City 

Schenectady 

Buffalo 

Chicago 

Omaha 

Average 

FOR COMPARISON 

Standard mixture. 



10.29 

8.91 

8.81 

9.61 

9.0G 

9.87 

10.97 

10.64 

11.75 

9.85 

10.32 

9.65 

9.24 

9.44 

9.89 



10.5 



9.72 
14.50 

8.38 
10.87 
10.93 
11.27 
12.13 
12.15 
14.46 
13.10 
11.91 
11.32 

9.33 
12.80 

11.63 



13.0 



6.45 
9.06 
9.48 
12.12 
12.77 
15.34 
16.39 
22.01 
35.32 
25.92 
29.19 
30.53 
35.95 
41.98 

21.61 



26.0 



42.06 
38.30 
41.26 
60.10 
49.06 
52.59 
34.14 
37.58 
26.19 
31.31 
39.38 
44.68 
38.83 
24.93 

40.03 



34.5 



31.48 

29.23 

32.07 

7.30 

18.18 

10.93 

26.37 

17.62 

12.28 

19.82 

9.20 

3.82 

6.65 

10.85 

16.84 



16.0 



= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 
= 100% 

= 100% 



= 100% 



These surfaces present every variety of grading in their com- 
position and it is apparent that they could not all be satisfactory. 
Evidently no system was carried out in their production. The 
percentage of bitumen varies from 8.8 to 11.7, probably not from 



SURFACE MIXTURES. 315 

carelessness entirely but because the mineral aggregate would 
permit of the use of a large amount in certain cases and less in others. 
The amount of filler or 200-mesh dust is deficient in many cases, 
although in some it seems high enough, owing to the presence of 
sand of 200-mesh size which, as will appear, does not act as filler. 

As will be shown later, the amount of 100- and 80-mesh material 
is deficient in the first seven cities and unbalanced in all. The 
grains of 10-, 20-, and 30-mesh sizes are present in far too large a 
degree in Washington, Louisvile, Newark, and New York, and are 
not well regulated in most of the cities. In fact the mineral aggre- 
gate in none of these towns was, at that time, well graded. 

If the records of the Barber Asphalt Paving Company are 
studied for the 10 years before 1899, as summarized in the following 
tables, the reason for the varied composition of the preceding 
mixtures is explained. All sorts of sands were used, and probably, 
although there are no records, all kinds of filler. See results tabu- 
lated on pages 316, 317, 318, and 319. 

If the average grading of the sand and of the mineral aggregates 
of these same cities be examined as far as the incomplete data will 
admit, the peculiarities of this part of the surface mixture are 
apparent. As fine sieves were not in use in the early days of the 
industry our knowledge of the grading of the finer part of the 
aggregate is limited, but in the sands of 1889 it is readily seen that 
in that used in Chicago there were not enough coarse particles, 
while the Newark and New York sands were only fit for concrete. 
Buffalo was deficient in 80- and 100-mesh particles, as were Kansas 
City, Louisville, and Washington. Other defects were apparent 
in this and the following years, to which it is unnecessary to call 
attention here, as the data are open to examination in the tables 
and the most striking points have been marked with asterisks. 
In 1893, for instance, all the sands were much too coarse except 
: n Buffalo and Chicago. In 1894 they were much better. It is 
sufficient to say that up to 1894 no effort based on any well-defined 
reasons had been made to regulate the grading of the sand in 
surface mixtures or to accommodate the dust and asphalt cement 
to the demands of the latter, although it had been determined in 
1892 that in the better class of pavements the sand was fine. 



316 



THE MODERN ASPHAL1 PAVEMENT . 



AVERAGE SANDS. 

1889. 



City. 


Passing 


Ret. 10 


70 


50 


40 


30 


20 


10 


Boston 


8* 
29 
20* 
12* 

6* 

10 
41 

28 
9* 


50 
49 
22 
43 
10 

15 
33 

31 
10* 


26 
16 
18 
22 
11 

15 
10 

17 
24 


11 
5 
20 
12 
17 

20 

8 

10 
30f 


3* 
1* 

13t 

5 
23 

18 
3 

7 
19f 


1* 
0* 
7 
3 
27 

18 
2 

6 
6 




Buffalo 1-B 


o 


Chicago 





Kansas City 


1 


Louisville 


1 


Newark 


6 


New Orleans 




New York 


4 


Omaha 


1 


St. Louis 




Scranton 


1 


Washington 


3 







1891. 











Passing 








City. 














Ret. 10 


















200 


70 


50 


40 


30 


20 


10 




Boston 


5 
9 


38 
45 


19 
32 


11 

6 


10 
3* 


10 
1* 


8t 
2* 





Buffalo 1-B 


1 


Chicago 


4 


11 


24 


21 


18 


12 


9 


1 


Kansas City 


3 


21 


18 


14 


17 


14f 


12f 


1 


Louisville 


















Newark 


4 


9* 


11 


10 


18 


23f 


23f 


3 


New Orleans 


















New York 


4 


23 


21 


16 


16 


10 


9 


2 


Omaha 


3 


16* 


20 


18 


27 


11 


5 





St. Louis 




Scranton 


5 


23 


16 


16 


14 


let 


Ht 





Washington 


4 


3* 


13* 


26 


29f 


16t 


7 


1 




*Too 


low. 




t 


Toobigl 


i. 







SURFACE MIXTURES. 



317 



MINERAL AGGREGATE. 

1892 











Passing 










City. 
















Ret. 10 


















200 


70 


50 


40 


30 


20 


10 




Boston 


18 
13 


21 
53 


11 
16 


14 
9 


14 
3 


let 

3 


6 
3 


1 


Buffalo 1-B 


3 


Chicago 


12 


29 


27 


16 


9 


6 


3 





Kansas City 


7 


6* 


7 


13 


20 


28f 


18f 


3 


Louisville 


12 


21 


20 


25 


13 


6 


3 





Newark 


7 


11* 


17 


22 


20 


18 


6 


1 


New Orleans 


6 


0* 


11 


39 


32 


11 


2 


1 


New York 


12 


21 


13 


14 


15 


15 


10 


3 


Omaha 


6 

7 


17 
13* 


10 
6 


13 
13 


15 
22 


21t 

29f 


17f 
12+ 


2 


St. Louis 





Scranton 


















Washington 


9 


6 


8 


30 


33 


12 


2 






1893. 



Boston 

Buffalo 

Chicago 

Kansas City. 
Louisville. . . , 

Newark 

New Orleans . 
New York. . , 

Omaha 

St. Louis. . . . 
Scranton. . . . 
Washington. . 



22 
51t 

47 
41 

16* 

24 
31 
28 

20* 



16 
27 
26 
16 

12 

10 
17 
14 

13 



17 
12 
14 
13 

17 

14 
13 
15 

23 



22 f 

5 

7 
11 

18 

19 
14 
17 

26 



20t 

3 

3 
10 

23 

19t 

14f 
17t 

13t 



5 
2 
3 

lot 

14 

14t 

lit 

9 

6 



1894. 



City. 








s Passing 








Ret. 10 


100 


70 


50 


40 


30 


20 


10 


Boston 


16 
17 
15 

29 

15 

21 

18 

11 


22 
30 

19 
21 

8* 
28 

15 
5* 


25 
34 
33 
24 

19 
23 

27 
12 


15 

12 

14 

9 

13 

10 

14 
20 


14 
4 

7 
7 

14 

8 

9 
31t 


8 
2 
5 
5 

14t 
6 

8 
17t 


2 
2 
5 
5 

14t 

4 

11 
5 




Buffalo 




Chicago 




Kansas City 

Louisville 

Newark 

New Orleans 

New York 

Omaha 




St. Louis 

Scranton 

Washington 





♦Too low. 



t Too high. 



318 



THE MODERN ASPHALT PAVEMENT. 



MINERAL AGGREGATE. 

1895. 



City. 



Boston 

Buffalo 

Chicago. . . . 
Kansas City. 
Louisville. . . 
Newark. . . . 
New Orleans 
New York. . 

Omaha 

St. Louis. . . 
Scranton. . . 
Washington. 



Passing 



100 



24 
18 
22 
27 
17 
16 
18 
21 
21 

19 



70 



17 

32 

19 

19 

16 

12* 

14* 

15* 

22 

12* 



50 



21 
30 
26 
24 
33 
17 
25 
15 
21 

21 



40 



14 
9 
12 
10 
14 
14 
19 
12 
11 

17 



30 



11 

3 

6 

7 

9 

14 

13 

13 

9 

13 



20 



4 

6 

8 

6 
14f 

8 
12f 

6 

11 



10 



7 

5 

9 

5 

4 
14f 

2 • 
13t 

7 

8 



Ret. 10 



Boston 

Buffalo 1-B. . 

Chicago 

Kansas City. 
Louisville. . . . 

Newark 

New Orleans. 
New York . . . 

Omaha 

St. Louis. . . . 
Scranton. . . . 
Washington. . 



1896. 









Passing 








City. 














230 


100 


80 


50 


40 


30 


23 


10 


Boston 


12.1 

7.4 


14.4 
6.2 


14.3 
20.1 


27.0 
49.3 


11.0 
8.1 


9.2 
3.8 


6.0 
2.1 


6.0 


Buffalo 1-B 


3.0 


Chicago Pit. 1. .. . 


9.9 


13.7 


18.8 


31.1 


9.2 


6.5 


5.2 


5.6 


Kansas City 


13.7 


8.7 


17.5 


40.6 


6.7 


5.3 


3.6 


3.9 


Louisville 


12.2 


5.4* 


12.6 


53.8 


8.1 


3.7 


2.0 


2.1 


Newark 


11.2 


8.9* 


10.2 


25.0 


14.8 


12.9 


8.4 


8.6 


New Orleans 


11.6 


9.4* 


11.3 


31.6 


14.7 


12.5 


6.0 


3.0 


New York 


14.4 


11.6 


11.9 


25.5 


13.3 


10.6 


6.5 


6.2 


Omaha 


10.6 
15.9 


11.9 

10.4 


20.3 
14.6 


33.8 
36.6 


9.2 

11.4 


6.5 
6.8 


4.1 
^5.9 


3.5 


St. Louis 


1.2 


Scranton 


11.0 


9.5* 


12.3 


29.1 


15.0 


12.3 


6.6 


4.2 


Washington 


8.7 


6.7* 


10.4 


31.2 


20.1 


14.7 


5.4 


2.8 



1897. 



16.5 
15.3 
15.7 
21.1 



14.9 



17.3 
14.1 
18.4 
14.6 
23.2 
13.7 
11.4 



14.9 

12.6 

16.4 

14.6 

6.4* 

12.2 

11.1 

14.5 

14.0 

12.7 

9.0 

8.4 



12.5 

16.3 

19.5 

15.3 

10.5 

9.8* 

9.9* 

13.9 

17.5 

18.2 

11.5 

7.5 



26 

46 

36 

34 

54 

27. 

28.9 

27.7 

35.5 

32.1 

31.1 

27.1 



10.1 

5.7 

5.0 

5.1 

7.5 

10.5 

13.3 

9.4 

7.4 

6.7 

12.3 

17.2 



8.5 


5.2 


5.7 


2.5* 


0.8* 


0.5* 


2.7* 


2.7 


1.7 


3.6 


2.9 


2.7 


3.2 


1.8 


1.2 


10.9 


7.2 


4.8 


11.6 


6.6 


4.5 


8.0 


4.6 


3.5 


5.6 


2.9 


2.5 


3.8 


2.0 


1.2 


11.8 


5.9 


4.6 


13.4 


9.5f 


5.4 



* Too low. 



t Too high. 



SURFACE MIXTURES. 



319 



MINERAL AGGREGATE. 

1898. 



City. 



Boston 

Buffalo 1-B. 
Chicago. . . . 
Kansas City. 
Louisville. . . 
Newark. . . . 
New Orleans 
New York . . 

Omaha 

St. Louis. . . 
Scranton. . . 
Washington. 



Passing 



200 



16.4 
15.8 
14.6 
16.2 
16.7 
12.9 
12.3 
15.3 
13.0 
14.9 
13.8 
13.8 



100 



15.2 
14.3 
17.3 
13.6 
11.8 
12.5 

8. 7* 
14.6 
15.6 
10.9 
12.0 

9.3 



80 



14.3 
19.2 
14.8 
15.6 
11.3 

8.4* 
11.1 
15.0 
19.2 
16.6 
11.7 

8.6 



50 



28.3 
40.1 
37.6 
31.9 
34.3 
20.6 
34.6 
25.3 
32.9 
41.9 
29.7 
29.1 



40 



11.0 

6.1 

9.4 

8.3 

10.9 

14.4 

15.8 

11.2 

8.0 

6.4 

13.2 

20.0 



30 



7 
2 
3 
6 
7 
12.0 
11.1 
8.5 
5.3 
4.3 
9.9 
10.7 



20 



4.4 



4.1 
6.3 
3.6 
3.0 
5.6 
5.2 



10 



2.9 
0.1 
0.7 
3.1 
4.0 
7.6 
2.3 
3.9 
2.4 
1.9 
3.9 
3.2 



1899. 



Boston 


16.2 
14.7 


13.6 
11.8 


10.4 

18.7 


24.9 
41.6 


15.7 

7.0 


8.4 
2.8* 


6.4 
1.9 


4.4 


Buffalo 1-B 


1.5 


Chicago 


12.9 


16.0 


17.3 


38.5 


8.5 


3.1* 


2.0 


1.6 


Kansas City 


13.5 


10.3 


15.5 


43.9 


7.9 


4.0* 


3.0 


1.9 


Louisville 


17.4 


8.0* 


5.1* 


41.3 


21.6 


3.4* 


2.0 


1.2 


Newark 


16.2 


15.2 


10.7 


12.9 


12.5 


10.8 


11.7 


9.9 


New Orleans 


14.0 


12.4 


10.4 


28.4 


19.0 


7.7 


5.7 


2.4 


New York 


14.5 


14.2 


14.1 


26.7 


13.5 


7.4 


5.9 


3.7 


Omaha 


14.8 
13.8 


14.7 
13.7 


13.9 
12.3 


28.6 
33.2 


12.9 
12.7 


6.3 
6.0 


5.2 

4.8 


3 6 


St. Louis 


3.5 


Scranton 


14.5 


12.9 


12.2 


25.6 


16.7 


8.6 


5.8 


3.7 


Washington 


14.2 


8.5* 


5.8* 


19.5 


22.4 


11.2 


9.8 


8.5f 



* Too low. 



t Too high. 



Bitumen in the Surface Mixtures of the Earlier Days of the 
Industry. — Up to 1896 the bitumen in surface mixtures was very 
variable in amount, and, as a rule, too low, owing probably to 
the necessity of keeping it at such a point because of the poor 
sand grading and the absence of binder, to avoid displacement 
of the street surfaces. The following tables show the average 
and extreme per cents of bitumen in the surfaces laid by the Bar- 
ber Asphalt Paving Company in a number of cities during the 
earlier years of which records are available. 



320 



THE MODERN ASPHALT PAVEMENT. 



AVERAGE AND EXTREME PERCENTAGES OF BITUMEN IN 
SURFACES OF THE BARBER ASPHALT PAVING COMPANY 
FOR ELEVEN YEARS, 1889-1899. 



City. 

Boston 

Buffalo 

Chicago 

Kansas City 

Louisville 

Newark » . . 

New Orleans. 

New York 

Omaha 

St. Louis 

Scranton 

Washington 

Average 



1889 



9 3-10.9 

10.0 
8.4-12.2 

9.8 
8 . 6-10 . 5 

9.8 
8.0-12.3 

9.9 

10.4-11.5 

10.7 

6.7-10.7 

9.0 
8.1-10.6 

9.2 
8.4-12.9 

10.8 
8.5-11.0 

9.8 
9.6-11.2 

10.1 
8.5-11.2 

10.1 

8.8-15.5 

9.8 

9.9 



1890 



7.6-12.2 

10.2 
9.0-11.5 

10.1 
8.0-11.1 

9.3 

7.8-10.7 

9.3 



.6-12.7 
10.8 
.6-12.4 
10.2 



8.8-11.6 

10.6 
9.1-11.4 

10.2 

10.1 



1891 



8.9-14.5 

11.1 
8.1-12.5 

10.0 
7.9-11.7 

9.5 
7.7-11.7 

10.2 

10.1-12.1 

10.9 

6.9-13.0 

9.6 



7.9-13.1 

10.6 

8.0-11.6 

9.8 



8.2-14.2 

10.5 
8.7-11.5 

10.3 

10.2 



1892 



8.6-12.0 

10.2 
7.2-15.9 

10.1 
8.8-11.5 

10.1 
8.9-12.3 

10.3 
8.9-10.8 

9.6 
7.8-10.9 

9.8 
8.8-10.4 

9.5 
8.3-11.7 

10.1 
7.7-11.5 

9.4 
9.6-12.8 

9.7 
9.2-12.2 

10.6 

8. 8-12. S 

10.7 

10.0 



1893 



9.3-10.3 

9.8 
8.1-13.7 

10.3 
9.2-11.7 

10.3 
9.0-11.3 

10.2 



9.2-10.2 
9.7 



8.9-13.4 

10.5 
8.8-9.8 

9.4 
7.3-11.7 

9.7 



9.6-10.9 
10.2 



10.0 



City. 



Boston 

Buffalo 

Chicago 

Kansas City. . 

Louisville 

Newark 

New Orleans . . 
New York .... 

Omaha 

St. Louis 

Scranton 

Washington. . . 

Average 



1894 



8.4-10.0 

9.4 
6.9-11.9 

10.0 
8.2-11.7 

9.8 
8.0-12.1 

9.9 



8.5-10.2 

9.4 
8.4-11.7 

10.1 
8.1-9.9 

9.0 



9.9-11.9 

10.6 

10.1-11.0 

10.5 

9.9 



1895 



5-11. 

9.9 
3-10. 

9.4 
4-11. 

9.9 
3-10. 

9.3 
0-11. 
10.0 
8-10. 

9.3 
1-10. 
10.0 
9-11. 

9.9 
4-10. 

9.1 



5-10 
9.4 



9.6 



1896 



8.7-11. 
9.9 
. 7-10 . 
9.7 
.5-11. 
10.2 
.4-10. 
9.4 
9.1-11. 
10.3 
9.3-11. 
10.3 
9.0-11. 
10.2 
9.2-11. 
10.5 
7.3-10. 

9.4 

9.0-11. 

9.9 

9.3-11. 

10.2 

9.2-12. 

10.8 

10.1 



1897 



9.0-11 

10.1 
9.3-11 

10.4 
9.4-11 

10.8 
9.5-11 

10.4 

9.2-10 

9.8 

8.0-11 

10.2 
9.0-11 

10.1 
9.6-12 

10.7 

8.1-11 

9.1 

9.4-11 

10.5 
10.0-11 

10.4 
9.1-12 

10.8 

10.3 



1898 



9.8- 



9 



9.3-11 

10.6 

9.6-11 

10.4 

-11 

10.5 

3-11 

10.4 

9.2-10 

9.9 

9.1-11 

JO. 2 

9.3-10 

10.0 

9.3-11 

10.5 

7.9-11 

9.0 

10.4-12 

11.3 

10.0-11 

10.2 

11.5-13 

12.1 

10.4 



.4 



.2 



1899 



9.4-11.5 

10.7 
8.6-11.6 

10.4 
9.2-11.7 

10.6 
9.3-11.3 

10.4 
9.5-11.7 

10.7 
9.3-10.6 

9.9 
9.0-11.6 

10.3 
9.0-12.1 

10.5 
8.2-11.1 

9.5. 
9.9-11.3 

10.7 
9.4-11.6 

10.4 
9.7-13.0 

10.8 

10,4 



SURFACE MIXTURES. 



321 



Since 1896 these irregularities in bitumen have grown smaller 
and the average percentage of bitumen higher, as can be seen 
from the average percentage of bitumen in the mixtures laid under 
the author's supervision as long ago as 1897: 

AVERAGE COMPOSITION, SURFACE MIXTURES, 1897. 



City. 



Bronx. 



St. Louis, Mo , 

Kansas City, Mo. . . . 

Elmira, N. Y 

Chicago, 111 , 

New York, N. Y 

Buffalo, N.Y..4-B Pit... 
tt 3 _ B ti 

Niagara Falls, N. Y 

Boston, Mass 

New York, N. Y. 

Yonkers, N. Y * 

Newark, N. J 

Jersey City, N. J 

Sioux City, Iowa 

Saginaw, Mich 

Buffalo, N. Y., 1-B Pit 
New Orleans, R.R. Pit. 

Detroit, Mich 

Pittston, Pa 

New Orleans, La 

Wilkesbarre, Pa 

Rockford, 111 

Scranton, Pa. 

Harrisburg, Pa , 

Washington, D. C. . . . 
Akron, Ohio , 

Average 



Bitu- 
men. 



10.5 
10.4 
10.9 
10.8 
10.7 
10.1 
10. C 
10.2 
10.1 
10.1 
10.5 
10.2 
11.4 
10.5 
10.0 
10.4 
10.6 
10.8 
10.6 
10.1 
10.5 
10.1 
10.4 
10.3 
10.8 
11.1 

10.5 



Passing Mesh. 



200 



100 



80 



16.3 

13.7 

25.6 

16.5 

12.4 

14.4 

11.1 

13.2 

11.2 

9.2 

10.7 

8.8 

13.9 

9.8 

7.8 

14.6 

10.8 

13.7 

12.8 

8.9 

8.5 

7.3 

10.3 

5.0 

6.7 

12.7 



50 



40 



6. 

4. 

2. 

4. 

8. 

4. 

7. 

6. 

9. 
10. 

9. 

9. 

8. 

9. 
15. 

5. 
11. 

4. 

7. 
11. 
13. 
15. 
11. 
19. 
15. 



30 



3.4 
3.4 
1.0 
2.4 
7.1 
1.9 
2.5 
2.9 
7.6 

10.2 
7.5 
9.8 
6.3 
8.1 
8.7 
2.1 

10.2 
2.4 
7.1 

10.4 
9.7 

12.2 

10.6 
6 

12.0 
5.9 



20 



1.8 
2.6 
0.3 
1.5 
4.1 
0.6 
0.8 
0.6 
4.7 
5.6 
4.3 
6.5 
4.0 
4.2 
2.1 
0.7 
6.5 
1.7 
3.2 
5.9 
6.3 
2.7 
5.3 
2.8 
8.5 
1.9 



10 



d 

CD «-i 






63° 
61° 
75° 
56° 
58° 
61° 
67° 
63° 
59° 
62° 
58° 
58° 
55° 
61° 
56° 
61° 
51° 
57° 
51° 
45° 
51° 
54° 
57° 
63° 
60° 
57* 

58° 



♦Retained on 10-mesh, .5%. 

Experience has shown, however, that in these surfaces, although 
the average percentage of bitumen reached 10.5, it was in most 
cases too hard, averaging 58, which has resulted in some cracking. 
In subsequent years, therefore, it has been the practice to use 
softer asphalt cement. The results have been very satisfactory. 

Too small an amount of bitumen in a mixture permits the 
easy entrance or absorption of water, which eventually disin- 
tegrates and rots the surface. It reduces the tensile strength 



322 THE MODERN ASPHALT PAVEMENT. 

and prevents the accommodation of the surface to the contrac- 
tion of the mineral aggregate, which follows a rapid fall of tem- 
perature, as this can only be met by the elongation of the bitu- 
men. In both of these ways lack of bitumen is a direct cause of 
cracking and deterioration of pavements. 

Analyses of specimens of old surface from Omaha, grouped 
and arranged according to their condition, show that the badly 
cracked pavements in that city contain the least bitumen and 
the better pavements the most, as appears from the following 
figures : 

AVERAGE BITUMEN IN OMAHA ASPHALT SURFACES. 

Good 10.0% 

Medium 9.4 

Badly cracked 8.6 

The results of the examination of the surfaces collected in 
1894 and of the data available at that time having shown nothing 
more than the fact that there was no uniformity in the way the 
mixture was made before then, and that it would be necessary 
to extend the investigation still further to find which was the 
most desirable composition, this work was continued as oppor- 
tunity offered during a period extending over two years and with 
extremely interesting results, which were published in Bulletin 
No. 1 of the Office of the Superintendent of Tests of the Barber 
Asphalt Paving Company, in March 1896, the substance of which 
was as follows: 

" The attention of the author was attracted, as long ago as 

1889, to a particularly good asphalt surface on Vermont Avenue, 

in Washington, D. C, which, although subjected to light traffic, 

had had scarcely a repair after, at that time, ten years' service. 

An analysis of this surface gave the following results: 

"Bitumen 11 .3% 

Passing 200-mesh sieve 16.0 



100- 


< i ( 


80- 


C I i 


50- 


( ( t 


40- 


I ( I 


30- 


( ( i 


20- 


11 I 


10- 


11 I 



.7 
5.2 
32.0 
16.4 
6.0 
2.7 
1.7 



100.0 
Density 2. 18 



SURFACE MIXTURES. 



823 



" The high percentage of bitumen and of dust, both unusual 
at the time the surface was examined, led to the conclusion that 
the desirable properties of this surface were due to the presence 
of plenty of bitumen and dust. In order to confirm this, several 
other surfaces were selected in Washington which were typically- 
good or bad, and it was found that the best were characterized 
by a similar composition to that of the Vermont Avenue surface, 
while the inferior were deficient in both asphalt cement and dust. 
An inquiry as to the conditions under which the Vermont Avenue 
surface was laid showed that the sand in use was from a pit and 
contained much fine material, on which account it was eventually 
abandoned. 

" In 1893 attention was called to the excellent character of 
the asphalt surface on Court Street in Boston, which had sustained 
successfully a very heavy traffic. The surface mixture was 
examined by the author and found to have the following compo- 
sition : 

"Bitumen 11 .7% 

Passing 200-mesh sieve 14.5 



< I 


100- " 


It 


80- " 


it 


50- " 


tt 


40- " 


It 


30- " 


tt 


20- " 


tt 


10- " 



11.2 

24.1 

20.5 

5.8 

4.6 

4.0 

3.6 

100.0 
" In this mixture high percentages of bitumen, of dust and of 
fine sand were found, which was in confirmation of the original 
conclusion that the Vermont Avenue surface in Washington wore 
well because it contained high percentages of these materials. 
These results led to the suggestion that the inquiry should be 
extended to a collection of representative surfaces from various 
parts of the country. This was undertaken and led to the same 
general conclusion, namely, that surfaces carrying the most bitu- 
men and dust or filler are the most satisfactory. 

" In 1895 the inquiry was extended still further, and an exam- 
ination of the street surfaces laid in a western city during the 



324 



THE MODERN ASPHALT PAVEMENT. 



period extending from 1888 to that year, some of which were much 
more satisfactory than others, was made. The results of the 
analyses of surfaces representing different years' work were as 
follows : 





1888 


1889 j 1890 


1891 


1892 


1893 


1894 


1895 


"Bitumen 


9.85 


10.35 Q.35 


9 05 


10 55 


9 85 


9 35 


9 50 


Passing 200-mesh sieve. . . . 


9.00 


9.60 


7.50 


10.60 


9.25 


9.00 


11.40 


10.95 


" 100- " " .... 


8.80 


25.45 


10.10 


9.60 


5.80 


6.30 


16.60 


13.95 


80- " " .... 


10.20 


23.05 


10.50 


14.50 


6.65 


5.40 


16.30 


17.50 


50- " " .... 


26.00 


20.05 


20.00 


30.20 


26.50 


36.30 


21.50 


31.00 


" 40- " " .... 


12.30 


4.55 


12.70 


8.20 


14.40 


10.80 


6.10 


4.95 


30- " " .... 


11.90 


4.05 


13.90 


6.90 


12.55 


8.20 


7.80 


6.40 


20- " " .... 


6.60 


2.80 


7.60 


5.00 


8.25 


6.50 


6.00 


2.70 


10- " " .... 


3.35 


2.10 


8.35 


5.95 


6.05 


7.65 


4.95 


3.08 



"If these results are grouped more closely, calling 200-mesh 
material dust, 100- and 80-mesh material fine sand, 50- and 40-mesh 
medium, and 30-, 20-, and 10-mesh coarse sand, the analyses catch 
the eye more quickly. 





1888 


1889 


1890 


1891 


1892 


1893 


1894 


1895 


" Bitumen 


9.85 

9.00 

19.00 

40.30 

21.85 


10.35 

9.60 

46.50 

24.60 

8.95 


9.35 

7.50 

^0.60 

32.70 

"9.85 


9.05 
10.60 
24.10 
38.40 
17.85 


10.55 
9.25 
12.45 
40.90 
26.85 


9.85 

9.00 

11.70 

47.10 

22.35 


9.35 
11.40 
32.90 
27.60 
18.75 


9.50 


Dust 


10.95 


Fine sand 


31.45 


Medium sand 


35.95 




12.18 









"The characteristics of these surfaces as noted on the streets 
were: 

" 1888. ... Soft; pushes and calks. 

1889 Considered one of the best mixtures. 

1890 Calks badly. 

1891 Calks badly. 

1892 Calks badly. 

1893 Calks worst of all; very mushy. 

1894 Hardly marked; very stable. 

"The 1894 mixture is the only one which has produced a surface 
which is reasonably free from calking in hot weather. Of the 



SURFACE MIXTURES. 325 

1895 surfaces we cannot judge until another year, although they 
at present are very promising and probably quite as good as those 
of 1894. x The 1889 surfaces are in better form than the surfaces 
of years prior to 1894. Those of 1891, 1892, and 1893 are so yield- 
ing as to be a mass of calk marks in summer. How this occurs is 
seen from the differences which are brought out by analyses. The 
1888, 1890, 1891, 1892, and 1893 surfaces are deficient in fine sand 
as compared to those of 1894, and this is especially the case with 
those of 1892 and 1893, where there is but 12.45 and 11.70 per cent, 
respectively, of fine material. They do not carry enough sand 
grains of this size to make the surface dense, and of course con- 
versely they have too much coarse material. It is apparent, there- 
fore, that, with the available sand, the grading must be so arranged 
that the coarse part shall not run as high as 20 per cent, preferably 
about 15 per cent, and the fine shall reach about 30 per cent, the 
dust being about 11 per cent, to give a stable surface. The bitumen 
in these mixtures is too low when compared with the amount found 
necessary for good surfaces in most cities, but here it was due to 
peculiarities in the sand, owing to which it will not carry more, 
and is therefore not as serious a defect as it would be in some 
other places. 

"As a whole the experience in this city was very encouraging 
in its confirmation of previous conclusions, and sufficiently so to 
render an attempt to follow them out in practice in other places 
desirable." 

The bulletin then goes on to present two illustrative cases 
where an explanation had been sought for the good or bad wearing 
properties of asphalt surfaces: 

" In New York there has been during the present winter (1896) 
some scaling of surfaces laid in the autumn of 1895, whereas others 
have shown nothing but the best results. Typical of these were 
surfaces on Fifth Avenue at Fifty-ninth Street and on Eighth 
Avenue at Twenty-eighth Street. Analyses were made of speci- 
mens of these surfaces, which quickly explained the differences in 
behavior. The results were as follows: 

1 At the present time it can be seen that the mixtures of 1895 have proved 
as desirable as it was expected they would. 



326 THE MODERN ASPHALT PAVEMENT. 

NEW YORK MIXTURE LAID IN 1895. 





Per Cent. 


Per Cent. 


" Bitumen 


9.8 
7.3 

5-9\ 14 7 
8.8/ 14 - 7 

24.4 

12.4 
9.1) 

10.7^30.6 

10.8) 
.8 


11.1 


Passing 200-mesh sieve 


9.8 


" 100- " " 


28.6 


" 80- " " 


" 50- " " 


" 40- " " 


6.6 


" 30- " " 


10.3 ) 


" 20- " " 


8.0 V25.3 


" 10- " " 


7.0 J 


Retained on 10-mesh sieve 










100.0 


100.0 



" The same striking contrast between a good surface and a 
poor one is here again well illustrated in the difference in bitumen 
and fine material in the two specimens. 

" Again the unsatisfactory surfaces from St. Louis, samples of 
which were sent in recently for examination, show that a coarse 
mixture is an inferior one and likely to scale. The results of an 
examination of the St. Louis surfaces were as follows. See results 
given in first two tables on page 327. 

"In this way the original conclusions of earlier years have 
been confirmed, and it has become the present policy to work upon 
the lines above indicated in laying surface. While nothing abso- 
lutely fixed can be suggested as a universal mixture, perhaps for 
the present the following may be considered as an ideal towards 
which to work. 

"Bitumen 10.0% or above 

Passing 200-mesh sieve 10 . 0% 



It 


100- 


{{ 


It 


80- 


(< 


it 


50- 


it 


it 


40- 


i t 


tt 


30- 


a 


tt 


20- 


tt 


tl 


10- 


tt 



10 


•0% 


tt tt 


10 


•0% 


tt tt 


20 


•0% 


It tt 


24 


•0% 


tl tt 


10 


0% 


tt tl 


8 


0% 


tt tl 


5 


•0% 


tl tt 


3 


0% 


tt It 



" The grading should not, apparently, be stretched too far as 
in such a case but little asphalt cement can be gotten in, and the 
surface will lack elasticity. 



SURFACE MIXTURES. 



327 



ST. LOUIS SURFACES OF 1892. 





Per Cent. 


Per Cent. 


u Bitumen 


9.7 

3 6 :s> 

6.9 

9.7 
17.7) 
20.2 [■ 56.5 
18.6) 

100.0 


10.0 


Passing 200-mesh sieve 


7.1 


" 100- " " 


io:S} 17 - 8 


80- " " 


" 50- " " 


19.0 


40- " " 


8.4 


11 30- " " 


13.9) 


" 20- " " 


12.4 V37. 7 


" 10- " " 


11.4) 








100.0 





ST. 


LOUIS SURFACES OF 1893. 






Per Cent. 


Per Cent. 


Per Cent. 


Per Cent. 


Per Cent. 


"Bitumen. 


9.2 


10.6 


9.4 


10.2 


9.3 


Passing 200 


2.8 


5.5 


7.0 


6.3 


6.6 


" 100 

80 


9-6\ 19 


l:l}i3.o 


8 5 i}l3.8 


1:1} 9- 9 


5.6\ 9 3 
3.7/ y,d 


50 


37.0 


27.3 


17.8 


18.4 


10.2 


40 


10.7 


11.1 


11.1 


12.7 


10.0 


30 


10.8 ) 

5.7 ^21.3 

4.8 ) 


15.3 ) 
9.6 V32.5 
7.6) 


18.1) 


15.5) 


21.1) 


20 


15.5 U0.9 


13.2 > 42.5 


20.4 V54. 6 


10 


7.3) 


13.8) 


13.1 ) 




100.0 


100.0 


100.0 


100.0 


100.0 



" Finally, it must be remembered that many mixtures which 

are quite different from the fine ones which have been mentioned 

have furnished good surfaces for light traffic. In Washington, D. C, 

for instance, a recent mixture (1896) analyzed as follows, and 

will, no doubt, serve entirely well there: 

"Bitumen 11.4% 

Passing 200-mesh sieve 7.2 



100- 
80- 
50- 
40- 
30- 
20- 
10- 



2.9 
3.1 
14.4 
16.9 
19.1 
16.4 
8.6. 

100.0 



" In the same way many coarse streets in Buffalo have served 
as well as could be desired. 



328 THE MODERN ASPHALT PAVEMENT. 

" In conclusion, attention must be called to the fact that a 
high percentage of bitumen is not safe in a mixture which is defi- 
cient in dust and fine sand, especially when it is to meet heavy 
traffic, because such a surface is unstable without the material 
which gives it stiffness and capacity to resist pushing and mark- 
ing. This is the reason the use of large percentages of asphalt 
cement in some cases has been the cause of trouble and has led 
to the use of mixtures deficient in asphalt cement for streets of 
heavy traffic. In most cases, with plenty of dust and fine sand, 
the per cent of asphalt cement in the mixture with steam re- 
fined Trinidad asphalt can be carried well above 15 per cent. 

" Clifford Richardson, 

" Superintendent of Tests. 

" Long Island City, N. Y., March 10, 1896." 

Soon after the appearance of this bulletin the author carried 
out the ideas contained in it in laying a Trinidad lake asphalt 
pavement, on the King's Road in Chelsea, London, England. 
The composition of this mixture was as follows: 

Bitumen. 10.8% 

Passing 200-mesh sieve 13 . 6 

100- " " 7.3 

" 80- " " 22.5 

" 50- " " 25.5 

" 40- " " 8.9 

30- " " 6.6 

" 20- " " 3.0 

" 10- " " 1.8 

100.0 

As this surface resisted entirely successfully the heavy traffic 
and fogs of London, where previous attempts with coarser sand 
and less filler had failed, it seemed to settle the fact that the con- 
clusions drawn in the bulletin were correct, and from that time 
to the present all the work under the supervision of the author 
on streets of much travel has been done with surface mixtures 
made on these lines. 

After the London work the next important surface which was 
laid was that on Fifth Avenue, in New York. This has proved 
successful. Its average composition is as follows: 



SURFACE MIXTURES. 



329 





Bitu- 
men. 








Passing Mesh 










200 


100 


80 


50 


40 


30 


20 


10 


1896 

1897 


10.8 
10.6 


15.4 
17.4 


10.5 
12.3 


10.7 
11.1 


22.3 
23.3 


10.9 

8.8 


8.9 
8.0 


4.9 

4.7 


5.6 
3.7 



FOR COMPARISON. 



London. . 10.8 



13.6 



7.3 



22.5 



25.5 



8.9 



6.6 



3.0 



1.8 



After from twelve to thirteen years' use the surfaces laid in. Lon- 
don and that on Fifth Avenue, New York, have proved them- 
selves most satisfactory. 

Since the year 1896 the asphalt pavements laid by the Barber 
Asphalt Paving Company have been constructed, as a rule, in a 
similar way to that which has been described; but there has been a 
decided improvement in the character of the work with each suc- 
ceeding year, as can be seen by comparing the average com- 
position of mixtures laid in 1896 in several important cities with 
those laid in the same places in 1899 and in 1904. 

BITUMEN AND MINERAL AGGREGATE. 

1896. 



City. 



Boston 

Buffalo 1-B 

Chicago Pit. 1. ... 

Kansas City 

Louisville 

Newark. 

New Orleans 

New York 

Omaha 

St. Louis 

Scranton 

Washington 

Average per cent. 



Bitu- 
men. 



9.9 

9.7 

10.2 

9.4 

10.3 

10.3 

10.2 

10.5 

9.4 

9.9 

10.2 

10.8 

10.1 



Passing Mesh 



200 100 



10.9 

6.7 

8.9 

12.4 

10.9 

10.0 

10.4 

12.9 

9.6 

14.3 

9.9 

7.F 



13.0 
5.6 

12.3 
7.9 
4.9 
8.0 
8.4 

10.4 

10.8 
9.4 
8.5 
6.0 



80 



12.9 
18.1 
16.9 
15.8 
11.3 

9.1 
10.1 
10.6 
18.4 
13.3 
11.0 

9.3 



50 



24.4 
44.4 
27.9 
36.7 
48.3 
22.4 
28.3 
22.8 
30.6 
33.0 
26.1 
27.8 



40 



9.9 

7.3 

8.3 

6.1 

7.3 

13.3 

13.2 

11.9 

8.3 

10.3 

13.5 

17.9 



30 



8.3 

3.4 

5.8 

4.8 

3.3 

11.6 

11.2 

9.5 

5.9 

6.1 

11.0 

13.1 



20 



5.4 
1.9 
4.7 
3.3 
1.8 
7.5 
5.4 
5.8 
3.7 
2.6 
5.9 
4.8 



10 



5.4 
2.7 
5.0 
3.5 
1.9 
7.7 
2.7 
5.5 
3.2 
1.1 
3.8 
2.5 



330 



THE MODERN ASPHALT PAVEMENT. 



BITUMEN AND MINERAL AGGREGATE. 

1897. 



City. 



Boston 

Buffalo 1-B 

Chicago 

Kansas City. . . . 

Louisville 

Newark 

New Orleans .... 

New York 

Omaha 

St. Louis 

Scranton. . * . . . . 
Washington 

Average per cent 



Bitu- 
men. 



10.1 
10.4 
10.8 
10.4 

9.8 
10.2 
10.1 
10.7 

9.1 
10.5 
10.4 
10.8 

10.3 



Passing Mesh 



200 100 



14.8 
13.7 
14.0 
18.9 
13.4 
15.5 
12.7 
16.4 
13.3 
20.8 
12.3 
10.2 



13.4 

11.5 

16.4 

13.1 

5.8 

10.9 

10.0 

12.9 

12.7 

11.4 

8.1 

7.5 



80 



11.2 

14.6 

16.5 

13.7 

9.5 

8.8 

8.9 

12.4 

15.9 

16.3 

10.3 

6.7 



50 



23.9 
41.5 
32.4 
30.9 
49.1 
24.5 
25.9 
24.7 
32.3 
28.7 
27.9 
24.2 



40 



9.1 

5.1 

4.5 

4.6 

6.8 

9.4 

11.9 

8.4 

6.7 

6.0 

11.0 

15.4 



30 



7 

2 

2 

3 

2 

9 
10.4 

7.1 

5.1 

3.4 
10.6 
12.0 



20 



4.7 
0.7 
.1.5 
2.6 
1.6 
6.5 
5.9 
4.1 
2.6 
1.8 
5.3 
8.5 



10 



4.3 
4.1 
3.2 
2.3 
1.1 
4.1 
4.8 



1898. 



Boston 

Buffalo 1-B 

Chicago 

Kansas City 

Louisville 

Newark 

New Orleans 

New York 

Omaha 

St. Louis 

Scranton 

Washington 

Average per cent. . 



10.6 


14.7 


13.6 


12.8 


25.3 


9.S 


6.7 


3.9 


10.4 


14.1 


12.6 


17.2 


35.9 


5.5 


2.5 


1.4 


10.5 


13.2 


15.5 


13.2 


33.6 


8.4 


3.0 


1.9 


10.4 


14.6 


12.4 


14.0 


28.6 


7.4 


5.8 


4.0 


9.9 


15.0 


10.6 


10.2 


30.9 


9.8 


6.6 


3.4 


10.2 


11.6 


11.2 


7.5 


18.5 


12.9 


10.6 


10.4 


10.0 


11.1 


7.8 


10.0 


31.1 


14.2 


10.0 


3.7 


10.5 


13.7 


13.1 


13.4 


22.6 


10.0 


7.6 


5.6 


9.0 


11.8 


14.2 


17.5 


29.9 


7.3 


4.8 


3.3 


11.2 


13.2 


9.7 


14.7 


37.2 


5.7 


3.8 


2.7 


10.2 


12.4 


10.8 


10.5 


26.6 


11.8 


8.9 


5.2 


12.1 


12.1 


8.2 


7.6 


25.6 


17.6 


9.4 


4.6 


10.4 

















2.6 
0.1 
0.6 
2.8 
3.6 
6.8 
2.1 
3.5 
2.2 
1.7 
3.5 
2.8 



1899. 



Boston 

Buffalo 1-B 

Chicago 

Kansas City. . . . 

Louisville 

Newark 

New Orleans .... 

New York 

Omaha 

St. Louis 

Scranton 

Washington 

Average per cent 



10.7 


J4.5 


12.1 


9.3 


22.2 


14.0 


7.5 


5.7 


10.4 


13.2 


10.6 


16.7 


37.3 


6.3 


2.4 


1.7 


10.6 


11.5 


14.3 


15.5 


34.5 


7.6 


2.8 


1.8 


10.4 


12.1 


9.2 


13.9 


39.3 


7.1 


3.6 


2.7 


10.7 


15.5 


7.1 


4.6 


36.9 


19.3 


3.0 


1.6 


9.9 


14.8 


13.7 


9.6 


11.6 


11.3 


9.7 


10.5 


10.3 


12.6 


11.1 


9.3 


25.5 


17.0 


6.9 


5.1 


10.5 


13.0 


12.7 


12.6 


23.9 


12.1 


6.6 


5.3 


9.5 


13.4 


13.3 


12.6 


25.9 


11.7 


5.6 


4.7 


10.7 


12.3 


12.2 


11.0 


29.7 


11.3 


5. '4 


4.3 


10.4 


13.0 


11.6 


10.9 


22.9 


15.0 


7.7 


5.2 


10.8 


12.7 


7.6 


5.2 


17.4 


20.0 


10.0 


8.7 


10.4 

















4.0 
1.3 
1.4 
1.7 
1.1 
8.9 
2.2 
3.3 
3.3 
3.1 
3.3 
7.6 



SURFACE MIXTURES. 



331 



AVERAGE COMPOSITION SURFACE MIXTURE. 1904. 



City. 



Alexandria, La. . . . 

Allegheny, Pa 

Auburn, Ind 

Boston, Mass 

Buffalo, N. Y 

Chicago, 111 

Cincinnati, Ohio. . . 

Decatur, 111 

Des Moines, Iowa. . 

Detroit, Mich 

Ft. Dodge, Iowa. . . 

Ft. Wayne, Ind 

Grand Rapids, Mich 

Harrisburg, Pa 

Kansas City, Mo . . . 
New York, N. Y... 
Los Angeles, Cal. . . 

Louisville, Ky 

New Albany, Ind. . . 
New Orleans, La. . . 
Niagara Falls, N. Y 

Omaha, Neb 

Ottawa, Ont 

Pittsburg, Pa 

Sandusky, Ohio. . . . 

Seattle, Wash 

Spokane, Wash. . . . 

St. Louis, Mo 

St. Paul, Minn 

Tacoma, Wash 

Toronto, Ont 

Trenton, N.J 

Walla Walla, Wash. 
Wichita, Kan 

Average 



Bitu- 
men. 



10.0% 

11.2 

10.5 

11.2 

10.4 

10.5 

10.2 

11.4 

11.0 

10.7 

10.9 

10.6 

10.2 

10.6 

10.3 

10.9 

11.0 

11.2 

10.8 

10.1 

10.3 

10.9 

10.6 

10.4 

10.4 

12.3 

12.9 

11.3 

10.9 

11.9 

10.7 

10.5 

13.4 

10.3 

10.9 



Passing Mesh 



200 100 80 50 40 30 20 10 



11. 
12. 
12. 
12. 
17. 
11. 
12. 
15. 
12. 
10. 
12. 
11. 
11. 
13. 
21. 
14. 
12. 
15. 
17. 
10. 
12. 
13. 
15. 
12. 

8. 
12. 
11. 
15. 
14. 
12. 
16. 
10. 

7. 
11. 



0% 
8 



18% 

5 
13 
10 
12 
16 
11 
10 

9 
12 
12 
11 
11 

6 
18 
11 
14 
12 

7 

15 
11 

7 
20 

7 
13 
14 
14 
15 
12 
13 
21 

9 
14 
10 



7% 

9 
12 
12 

9 
17 
13 

8 
16 
12 
13 
12 
10 

8 
13 
10 
12 

8 

5 
13 
13 
13 
11 

6 
12 
11 
11 
14 
14 
10 
14 
14 
12 
16 



19% 

42 

28 

32 

25 

34 

29 

27 

30 

33 

27 

27 

23 

32 

16 

28 

20 

26 

23 

23 

26 

39 

27 

42 

28 

25 

22 

27 

31 

24 

27 

29 

27 

32 



15% 
11 

9 
12 

7 

5 
13 
11 

9 
10 
13 
14 
12 
15 

6 
13 
11 
13 
17 
14 
10 

6 

7 
12 
12 
11 

8 

6 
10 
13 

6 
14 

8 
10 



13% 

4 

6 

5 

4 

2 

6 

6 

8 

7 

6 

7 
11 

7 

6 

7 

8 

7 
12 

8 

9 

4 

4 

5 

7 

7 

9 

5 

5 



5% 

3 

4 

3 

3 

2 

3 

5 

3 

3 

3 

5 

6 

5 

6 

4 

8 

4 

6 

4 

3 

4 

4 

3 

5 

4 

7 

4 

2 

5 

1 

3 

9 



2% 

2 

5 

2 

7 

2 

2 

5 

2 

2 

2 

2 

4 

3 

3 

2 

4 

3 

2 

2 

4 

3 

1 

2 

4 

3 

5 

2 

1 

3 

1 

2 

1 



5% 



Oil ^ _j 



55° 

62 
68- 
64 
62 
61 
54 
63 
71 
72 
64 
66 
62 
66 

68 

53 

65 
54 
67 
69 
58 
67 
67 
80 
77 
75 
74 
76 
61 
73 
80 



The general improvement and greater uniformity reached by 
experience between 1896 and 1899 and 1899 and 1904 is marked 
in several particulars. The average per cent of bitumen in the 
more recent mixtures is at a far better figure, 10.9, because the 
grading in the late/ mineral aggregate is more satisfactory, since 



332 THE MODERN ASPHALT PAVEMENT. 

it holds more 200-mesh dust and, as a rule, a better percentage 
of 100- and 80-mesh sand. In some cases, of course, the sand 
grading could still be improved upon in this direction, but this is 
the case only where no suitable fine sand was available within 
reasonable distances, as in Washington and Louisville, while a 
falling off of the 100- and 80-mesh grains in New York in 1904 
is due to inability to find such sand, this material being derived 
in 1899 from ballast coming to the port, none of which is now to 
be had. The New York surface mixture of 1904 is, therefore, 
not as satisfactory as it was in the former years. 
• The New York mixture of 1899 was regarded at that time as 
an unexceptional one, and it was decided to consider it a standard 
for mixtures on streets of any traffic for the remainder of the country. 
In round numbers the composition of this mixture and of the sand 
of which it was composed, regardless of the small amount of 200- 
mesh material which it contained, was as follows: 

Sand. 

Bitumen 10.5% 

Passing 200-mesh sieve 13.0 

" 13.0 17.0% 



100- 
80- 
50- 
40- 
30- 
20- 
10- 



13.0 17.0 

23.5 30.0 

11.0 13.0 

8.0 10.0 

5.0 8.0 

3.0 5.0 



100.0 100.0 

With the object of explaining to the practical man, the super- 
intendent or yard foreman, the features of such a standard mix- 
ture it was considered from the point of view of consisting of a 
mineral aggregate composed of sand and dust and a proper per- 
centage of bitumen. The mineral aggregate must be regarded 
as being made up of three elements — the fine sand, which is the 
most important, the coarse sand, which is desirable, and the dust 
or filler, which is absolutely necessary. The mineral aggregate of 
a standard mixture may, therefore, be considered from the following 
points of view: 

1st point— 100- and 80-mesh sand 17 + 17 =34% 

2d ' ' —10-, 20-, and 30-mesh sand 10 + 8 + 5 = 23 

3d " —Filler + 200 sand. Dust + fine sand. . =17 



SURFACE MIXTURES. 



333 



Or for the complete surface mixtures: 

1st point— 100 and 80 sand 13 + 13 = 26% 

2d " —10, 20, and 30 sand 3 + 5 + 8 = 16 

3d " —Filler + 200 sand =13 

4th " —Bitumen =10.5 

Or these points may be expressed in one of the following ways. 

ASPHALT SURFACE MIXTURE. 

Bitumen 
10.5% 
(4th point) 



Correct surface 
mixture, 100% ' 



Mineral aggre- 
gate, 89.5% 
(1st point) 
(2d " ) 
(3d " ) 



Filler, 13.0% 
(3d point) 



Sand, 76.5% 
(1st point) 
(2d " ) 



Mesh. 

100.. 13.0) n „ n „ 

80..13.o[ 260 % 
(1st point) 

50 23.5% 

40 11.0% 

30... 8.0 ) 

20... 5. V 16.0% 

10. ..3.0) 
(2d point) 



ASPHALT SURFACE MIXTURE. 
Composition. 
Bitumen 10 . 5 — 4th point 



Filler+ 200 sand 13 .0— 3d point 

26.0— 1st point 



100 sand, 13.0 
80 " 13.0 



40..., 


30... 


.. 8.0) 


20... 


.. 5. OS 


10... 


.. 3.0) 



23.5 



11.0 



16.0— 2d point 



Sand, 
76.5% 



Mineral 
aggre- 
gate, 
89.5% 



Correct 

asphalt 

mixture, 

100% 



334 THE MODERN ASPHALT PAVEMENT. 

The surface mixture, therefore, may be regarded: 
1st. As a whole. 

2d. As a mixture of bitumen and a mineral aggregate. 
3d. As a mixture of bitumen, filler, and sand. 
4th. As a mixture of bitumen, filler, 100- and 80-mesh sand 
and 10-, 20-, and 30-mesh sand in suitable proportions. 
For example take a New York mixture: 
1st. New York mixture. 

2d. 10.5 per cent bitumen, 89.5 per cent mineral aggregate. 
3d. 10.5 per cent bitumen, 13.0 per cent dust, 76.5 per cent sand. 
4th. Bitu- 200 100 80 50 40 30 20 10 

men, Dust, < , > » , . 

10.5 13.0 26.0 23.5 11.0 16.0 

or 

10.5 13.0 13.0 13.0 23.5 11.0 8.0 5.0 3.0 

In forming an opinion, therefore, of an old or new surface mix- 
ture it becomes evident that the four points which have been de- 
scribed must be considered. These points may be differentiated 
from the composition of an old mixture or combined to form a 
new one. 

The primary consideration is the sand and the -first point that it 
shall contain a normal and sufficient amount of 100- and 80-mesh 
material. This was, and undoubtedly is to-day, the most essential 
feature in making a satisfactory mixture. It is essential because 
without this fine sand the mixture is porous and open, and more 
particularly because, unless it is present, a sufficient amount of dust 
or filler cannot be used. The fine sand prevents the dust from 
balling up and making a lumpy mixture and, as will eventually 
appear, the larger the amount of fine sand the more dust can be 
introduced without difficulty. In the earlier mixtures, 1880 to 
1896, a large percentage of dust could seldom be used, although 
the attempt was often made, as the resulting mixture was difficult 
to handle and rake. 

The second point or consideration lies also in the sand grading 
and is the regulation of the amount of the 10-, 20-, and 30-mesh 
sand grains. In the Fifth Avenue mixture this material amounted 



SURFACE MIXTURES. 335 

to 16 per cent. It was unavoidable there, owing to the character 
of the sand available, but was believed to be desirable in several 
ways. In the first place, it seemed to fill the place taken by broken 
stone in hydraulic concrete, and to carry the traffic, so to speak. 
In the second place, it gave a less slippery surface than a finer 
mineral aggregate. In both these ways the coarse material is 
desirable, but closer study and experience has shown that at times 
it may be reduced or largely omitted to advantage, especially in 
damp climates. 

To bring about a satisfactory arrangement of the first two points, 
or sand grading, one or more kinds of sand are necessary, usually 
more than one. For example, in the Fifth Avenue mixture the 
main sand supply was deficient in 100- and 80-mesh grains. It 
was, therefore, necessary to add a certain amount of fine sand 
consisting predominantly of grains of this size. 

The third point, and one also of great importance, is that the 
amount of filler or dust shall be sufficient. In the standard mix- 
ture of 1899 this was intended to reach, together with the small 
amount of 200-mesh sand and the natural filler present in Trinidad 
asphalt, 13 per cent. In the older, coarse Washington and St. 
Louis mixtures of the early nineties the filler and 200 sand rarely 
reached 7 per cent, and in St. Louis fell, at times, below 3 per 
cent. This was attributable to two causes: one, the fact that 
such coarse mixtures would not carry much dust without balling, 
and the other, because it was considered at that time uncertain 
if there were any merit in using a filler. We now know that dust 
gives stability to the mixture, aids in excluding water, and that 
the best surfaces are those which, up to a certain limit, contain 
the most filler. In the standard mixture of 1899 the largest amount 
of dust which such a sand grading could carry was about 13 per 
cent, owing to the relatively small amount of 100 and 80 sand 
grains. Beyond this percentage the mixtures would become 
greasy or would ball. 

With the first three points arranged in a satisfactory way, the 
fourth or last point was to decide on how much asphalt cement 
the mineral aggregate would carry. This has been determined 
in recent years by the pat test, described on pages 351 and 514, 



336 THE MODERN ASPHALT PAVEMENT. 

which readily shows whether an excess or deficiency in asphalt cement 
has been used. This test cannot, in all probability, be improved 
upon. If each grain of material in the mineral aggregate is coated 
with asphalt cement and the voids more than filled the excess 
will be squeezed out in making a pat and stain the paper exces- 
sively. If the voids are not filled the only stain on the paper 
will be a light one from the cement coating the grains of sand. A 
perfect mixture will contain just enough cement to fill the voids 
in the aggregate, stain the paper well but not excessively (Figs. 
8, 7, 8, and 9). The hotter the mixture the more liquid the 
asphalt cement and the freer the stain. Cold mixtures will give 
no indication, while the difference in the markings of a fine and 
coarse sand will be readily learned by experience. 

The preceding instructions are satisfactory for turning out 
a mixture for the conditions ordinarily met with if the available 
materials admit of following them, or for judging the character 
of old surfaces when they have been resolved into their constitu- 
ents by analytical methods. 

In cases where there may be an excess of fine sand, particu- 
larly of 200-mesh material, some modification of the method of 
procedure which has been described will be necessary. This 
will be taken up later. 1 

Work on the Old Rule-of-thttmb Basis. — In comparison with a 
standard mixture made according to the previous instructions 
work done without any rational method of control is instructive. 
Several such mixtures have been examined which were laid in 
Chicago in 1898 and 1899 by contractors exercising no technical 
supervision over their work. See first table on page 337. 

There is hardly a mixture among these that is not open to 
criticism in one respect or another, while that laid under the 
author's supervision could in itself be slightly improved. The 
mixtures are more or less deficient in coarse sand as compared 
with the standard adopted. This is general, if it is a defect, and 
is due to the character of the local sand. The Bermudez mixture 
is very deficient in bitumen and for no other reason except that 

1 See page 345. 



SURFACE MIXTURES. 



337 



enough asphalt cement has not been put in. It would easily 
carry more, as the sand is very fine, quite too much so. 
CHICAGO, ILL., MIXTURES OF 1898 AND 1899. 





Bitu- 
men. 


Passing Mesh 


go 




200 


100 


80 


50 


40 


30 


20 


10 




Bermudez asphalt 

Trinidad lake asphalt. . . . 

Alcatraz asphalt 

Standard asphalt 

Trinidad land asphalt.. . . 


8.9 
11.2 
10.3 

8.5 
10.8 


11.1 

12.8 

13.7 

8.5 

6.2 


20.0 
8.0 
5.0 
5.0 

18.0 


35.0 
11.0 

28.0 
28.0 
26.0 


20.0 
43.0 
37.0 
41.0 
31.0 


1.0 

7.0 
4.0 
7.0 
5.0 


1.0 
4.0 
2.0 
2.0 
1.0 


1.0 
2.0 
0.0 
0.0 
1.0 


1.0 
1.0 
0.0 
0.0 
1.0 


1.0 



Author's supervision . . 



FOR COMPARISON. 

|l0.6|ll.4|l4.o|l5.o|35.o| 8.o| 3.01 



The second mixture is one which is hardly open to serious 
comment. The mineral aggregate should have, however, rather 
more 80- and 100-mesh grains, so that they should together reach 
25 to 27 per cent. 

The Alcatraz has only 6 per cent of sand coarser than a 50-mesh 
sieve, and it is unbalanced in its 80- and 100-mesh sizes. 

The Standard mixture is very inferior and cannot prove sat- 
isfactory. It is very deficient in bitumen, dust, and 100-mesh 
sand, three of the important factors in a good wearing surface. 

The Trinidad land asphalt should have more filler, but it is 
not otherwise defective, in so far as the mineral aggregate is con- 
cerned, except in the usual absence of coarse sand. 

As a whole these mixtures are excellent examples of ordinary 
work done empirically and without proper control. 

In other cities even more glaring defects are often met, as can 
be seen from a few examples: 



Cities. 


Bitu- 
men. 


Passing Mesh 


200 


100 


80 


50 


40 


30 


20 


10 


Toronto, Canada. . . 

Utica, N. Y 

Indianapolis, Ind. . . 


8.4* 
8.0* 
9.9 


24.6* 
26.5* 
13.1 


22.0 
31.7 
3.0* 


12.0 
17.9 
3.0* 


22.0 

7.7 
24.0 


5.0 

5.6 

22.0 


3.0 

1.5 

12.0 


2.0 
0.8 
7.0 


1.0 
0.3 
6.0 



* The shortcomings are here marked with an asterisk. 



338 



THE MODERN ASPHALT PAVEMENT. 



That the cardinal points in a mixture were often neglected 
in the earlier days can also be seen from an examination of the 
materials and their proportions in a mixture sent out on August 8, 
1895, for use on Eighth Avenue in New York: 



SAND— COW BAY. (GOODWIN.) 

ing 200-mesh sieve Trace 

100- 



80- 
50- 
40- 
30- 
20- 
10- 



a 

5.0% 
13.0 
42.0 
37.0 

2.0 



DUST— TUBE-MILL. 
Passing 200-mesh sieve 66.0% 



100- 
80- 



20.0 
14.0 



ASPHALT CEMENT. 

Bitumen 65.0% 

PROPORTIONS. 

801 lbs 79.5% 

60 " ■.. 5.9 

147 " 14.6 



Sand. 
Dust. 
A.C. 



1008 



100.0 



A mixture made from the above materials in the proportions 
given would have about the following composition: 



Bitumen 9 . 5% — 4th point 

Passing 200-mesh sieve 8.9 





100- " 


<< 




80- " 


«< 




50- " 


«< 




40- " 


<< 




30- " 


« 


It 


20- " 


u 


at 


10- " 


tt 



1.3 1 
1.0 / 
4.1 
0.4 
13. 5-> 
59.6 [ 
1.7 J 



— 3d 

2.3— 1st 



64.8— 2d " 



100.0 



SURFACE MIXTURES. 339 

It is evident that none of the four points in a good mixture 
is approached in this one. It is deficient in fine sand, far too 
coarse, contains too little dust, and would not hold enough bitu- 
men. 

This is, of course, an exaggerated case, but much mixture of 
a similar description has been sent out and is being made to-day 
by ignorant contractors. 

Problems Arising from Lack of Sand Suitable for Obtaining 
the Standard Grade. — Our illustrations and experience have shown 
that at times the sands to be found in any locality do not permit 
of attaining the standard grade which has been proposed. For 
example, in Washington, D. C, there is no sand available which 
will supply the proper amount of 100- and 80-mesh material 
in sufficient amount. In other cities there may be an excess of 
200-mesh sand. Again, in some localities, coarse sand is an expen- 
sive article, and it is impossible to introduce into the mixture 
the normal amount of 10-, 20-, and 30-mesh grains at any reason- 
able cost. Finally, questions arise as to whether under some 
trying conditions a mixture cannot be made which is more resistant 
to unfavorable environment than the standard and as to whether 
sands of the same grading in different localities the grains of 
which may have a different surface and a different shape, and in 
consequence of the last fact may have different voids, can be 
handled in the same way as New York sand. The proper amount 
and the consistency of the asphalt cement to be used under vari- 
ous conditions must also be determined. These points have 
been so far settled by the results of investigations carried out 
during the last few years that the problems can now be discussed 
fairly intelligently. 

Mixtures Necessarily Coarser than Standard. — The City of 
Washington was once in a situation of this kind. Until recent 
years, there has been no available supply there of what is known 
as "tempering sand," and the surface mixture in use was on this 
account deficient, more or less, in 80 and 100 mesh grains. In 
the early days of the industry this deficiency was a serious one. 
The average composition of the surface mixture laid in 1889 was 
as follows: 



340 THE MODERN ASPHALT PAVEMENT. 

Density 2.10 

Bitumen 9.7% 



Pass 



ng 200-mesh-sieve 9.3 

3.0 

5.0 

20.0 

20.0 

18.0 

8.0 

7.0 



100 


it 


a 


80 


n 


tt 


50 


t< 


tt 


40 


tt 


tt 


30 


tt 


tt 


20 


tt 


tt 


10 


tt 


tt 



100.0 



This mixture is plainly deficient in 80- and 100-mesh sand 
grains, in the percentage of bitumen, and probably in filler or 
actual dust, since less than 4 per cent of ground limestone, of 
which not more than 60 per cent passes a 200-mesh sieve, was 
added to the mixture, although the 200-mesh material reaches 
9.3 per cent, more of this being in the form of sand grains than of 
dust, a condition which investigations to be described later will 
show has a decided effect upon the character of the mixture. 

The streets on which the surfaces of 1889 were laid were sub- 
jected to very light travel and were fairly satisfactory for that 
period, but when they were examined in 1894 it was evident 
that they could have been improved upon by the selection of 
a better mineral aggregate, containing more filler, and which, 
consequently, could carry more bitumen. 

Of recent years there has been a distinct imorovement 
in the grading of the mixture laid in Washington, as shown 
by the following analysis of the pavement laid by the Brennan 
Construction Company on Pennsylvania Avenue in 1907. 



PROPORTIONS. 

Asphalt cement (Beramdez) 102 lbs.= 11 .5% 

Limestone dust 55 ' ' = 6.2 

Sand 731 " = 82.3 



888 " =100.0% 



SURFACE MIXTURES. 341 



ANALYSIS. 

Bitumen 10.5% 

Sand, passing 100-mesh sieve 25 .0 

' ■ retained on 100-raesh sieve 10.3 

" " " 80 " " 12.4 

" " " 60 " " 26.6 

" " • " 40 " " 23.1 

" " " 20 " " ?.6 

In some other cities similar conditions are met with in regard 
to the available materials for making the mineral aggregate, and 
experience has shown that where the streets to be paved are care- 
fully drained and the traffic is not heavy such a mixture will prove 
satisfactory, although it is probable that if the standard grading 
had been employed with a cement which is somewhat softer than 
that which would be used on a heavy-traffic street the life of the 
pavement would be somewhat extended. 

On the other hand, it is the opinion of certain experts that a 
coarser mixture is more desirable for streets of light traffic, and 
that where the surface is not thoroughly rolled out and closed up 
thereby it is more satisfactory than a finer one. There is ,a possi- 
bility that this may be so if the finer standard mixture is not made 
with a softer asphalt cement, the experience of the author in 1896, 
in several western cities where streets were paved having no traffic 
at all, having shown that standard surface mixture laid with a rather 
hard cement cracked to a very considerable extent after two years. 
Where, however, a standard mixture was laid on such streets with 
a very soft cement, cracking has not taken place under the same 
conditions. For the reason that finer sands are not available in 
Washington, or in the belief that a coarser mixture is more desirable, 
the more recent specifications for asphalt pavements in that city 
call for a sand of the following grading: 



100-mesh At least 10% 

80- and 100-mesh " " 25% 

1 ' 10-, 20-, and 30-mesh ' ' ' * 15% 



342 



THE MODERN ASPHALT PAVEMENT. 



In view of the above facts, where fine sand is not to be pro- 
cured readily, a modified standard for sand grading and finished 
mixture has been adopted. 



STANDARD GRADING FOR LIGHT TRAFFIC. 





Sand. 


Mixture. 


Bitumen 




10% 
10 


Passing 200-mesh 




100- " 

80- " 


11 } 22% 


8}» 


50- " 


33 


26 


40- " 


15 


12 


30- " 


13] 


10] 


20- " 


10 ^30 


8 ^24 


10- " 


7J 


6J 




100 


100 



A very considerable amount of work which has proved entirely 
satisfactory in small cities and towns has been done on this basis 
under the author's supervision. Such mixtures would not, how- 
ever, be satisfactory in all large cities, except on residence streets, 
and it is because most of the mixtures of the careless contractor 
are never more satisfactory in their grading than this that they 
are not entirely successful in their work where it is subjected to 
heavy traffic. 

Excess of Fine Sand of ioo- and 8o-Mesh Size. — Where the 
regular sand supplies contain an excess of 100- and 80-mesh material, 
and where it is impossible to introduce into the mixture the normal 
amount of 10-, 20-, and 30-mesh grains at any reasonable cost, a 
new problem is brought to our attention. Such a situation is 
complicated by the fact that an excess of 100- and 80-mesh grains 
may or may not be accompanied by the presence of a large 
amount of 200-mesh material. 

If the 200-mesh material is not present the mineral aggregate 
\can, generally, be treated in much the same way as the standard 



SURFACE MIXTURES. 343 

grading, merely allowing for the fact that the greater surface exposed 
by the grains of the fine material necessitates the use of a larger 
percentage of asphalt cement. The resulting mixture may be 
quite satisfactory and, on the other hand, may possess less stability 
than it should and be more liable to cracking at low temperatures 
and to displacement. In other respects it may be preferable to 
the standard mixture, if sufficient filler is used, owing to the fact 
that the surface is a closer one than when the coarser particles are 
present. 

It may also be necessary to use sand in which, while the coarser 
particles are present in nearly normal amount, the distribution of 
the finer sand, the 80- and 100-mesh grains, may be quite different 
from that found in the standard grading. Such a condition will 
necessitate changes in the handling of such a sand, as will appear 
when the consideration of the amount of bitumen which a mineral 
aggregate will carry is arrived at, and this may be conveniently 
taken up at this point. 

The standard New York sand without 200-mesh material or 
filler should contain 17 per cent of grains passing the 100-mesh 
and 17 per cent passing the 80-mesh "screen, resulting in the pres- 
ence of only 13 per cent of each of these grades in the finished 
mixture. For the purpose of studying the effect of an alteration of 
the proportions of these two sands some sands have been made up 
on an experimental basis and the voids, weight per cubic foot, with 
and without filler, determined. See results tabulated on page 344. 

In the sand, both with and without filler, No. 1, the lack of 100- 
mesh grains and increase of 80 above the usual proportion causes 
an increase in the voids over those found in the standard New 
York grading. An increase in both 80- and 100-mesh grains 
to 5 and 6 per cent each above the normal, No. 5, reduces the 
voids decidedly with the plain sand and slightly when filler is present, 
but with all the other arrangements, while the sands alone may 
be improved, there are larger voids when the filler is present than 
in the normal mixture. It seems, therefore, that unequal amounts 
of 80- and 100-mesh are not desirable, but that perhaps larger 
amounts of both might be, since the voids, when 45 per cent of 
the two sands are present instead of 34 per cent, are reduced 



344 



THE MODERN ASPHALT PAVEMENT. 



WEIGHT PER CUBIC FOOT AND VOIDS IN NEW YORK SAND, 
WITH VARYING PERCENTAGES OF 100- AND 80-MESH 
MATERIAL. 





1 


2 


3 


4 


5 


N. Y. 

Regular 

Grading 

with same 

Sand. 


Passing 100-mesh sieve. . 
80- " " .. 
50- " " .. 
40- " "... 
30- " " .. 
20- " " .. 
10- " " .. 

Per cent 100-mesh grains. 

Weight per cubic foot 
with no 200o 


4% 
30 
31 
16 

8 
7 
4 

100 

Low 
High 

108.3 
35.1 

119.4 

28.5 


30% 

4 
31 
16 

8 
7 
4 

100 

High 
Low 

110.0 
34.1 

119.6 
28.3 


28% 
17 
26 
13 

7 

6 

3 

100 

High 
Normal 

110.0 
34.1 

118.9 

28.8 


17% 
28 
26 
13 
, . 7 

6 

3 

100 

Normal 
High 

111.5 
33.2 

119.0 

28.7 


22% 
23 
26 
13 

7 

6 

3 

100 

High 
High 

112.5 

32.8 

121.7 
27.1 


17% 

17 

30 

13 

10 

8 

5 

100 

Normal 
Normal 

109 9 


Voids 


34.2 


Weight per cubic foot 

with 13 per cent dust. . 

Voids 


120.4 

27 8 







slightly. The presence of so much fine material, however, it is 
feared, would make the mixture mushy, and in addition it is generally 
very difficult and expensive to accomplish this, since such material 
is not always available. More asphalt cement is also necessary to 
cover the fine grains, which makes the mixture more expensive, 
without an adequate return. 

The effect of such changes in the standard grading upon the 
percentage of bitumen which the mixture will carry is well illustrated 
by the analyses of the following mixtures which were turned out 
in New York under the author's supervisions in 1899. See table on 
page 345. 

It must be added, however, that some of the difference in 
the percentage of bitumen in these cases may be due to a variation 
in the shape or surface of the sand grains as well as to the grading, 
and that similar results might not be obtained with the same 
grading for sands from other localities. 



SURFACE MIXTURES. 



345 



NEW YORK MIXTURE— PAT PAPERS ALL WELL STAINED. 





Standard 
Average. 


A 


B 


c 


D 

Av. N. Y. 
Week 
Ending 


Date , 


N.Y., '99 


2-7-'00 9-20-'99 


2-28-'00 

765 
110 
167 

High 
Normal 

28% 
16 
37 
12 

3 

3 

1 

100 

11.3% 

14.7 
74.0 


8-26-'99 


Proportions : 

Sand 




790 

85 

149 

Low 
High 

12% 
24 
37 
15 

5 

4 

3 

100 

9.5% 

15.5 
75.0 


775 

100 

95 (Ber.) 

Normal 
Low 

19% 

9 
28 
20 
12 

7 

5 

100 

9.5% 

15.5 
75.0 




Dust 






Asphalt cement 






Remarks : 
Per cent of 100-mesh grains 

Passing 100-mesh sieve 

80- " " 

50- " " 

40- " " 

30- " " 

20- " " 

10- " " 

Bitumen 


Normal 
Normal 

17% 
17 
31 
16 

8 

7 

4 

100 

10.5% 

13.0 
76.5 


Normal 
High 

16% 
23 
38 
12 

5 

4 

2 

100 
10.4% 
12 1 


Dust and sand (passing 200 
sieve) 


Sand 


77 5 








100.0 


100.0 


100.0 


100.0 


100.0 



Effect of 200-Mesh Material. — In the case of sands which con- 
tain a very considerable amount of material passing the 200-mesh 
jieve the conditions will be found to be different from any of those 
which have been previously discussed. That portion of the sand 
which will pass a 200-mesh sieve may consist, as has been previously 
shown in considering pulverized mineral matter for use as a filler, 
of particles resembling sand and of more impalpable material, 
which may be considered as true dust or filler. The effect of a 
large proportion of 200-mesh grains in the sand on the surface 
mixture will depend largely, therefore, on whether they are sandy 
or fine enough to act as a filler, and also largely on the character 
of the sandy grains themselves, that is to say, their shape and 
surface. If the coarser 200-mesh grains are round a mixture con- 



346 THE MODERN ASPHALT PAVEMENT. 

taining any considerable amount of them, especially if the remainder 
of the sand is largely of 100- and 80-mesh size, will be very mushy 
and readily displaced. In 1901, in Kansas City, Mo., a mixture 
was turned out the sand of which contained as much as 14 per cent 
of sandy grains of 200-mesh size. With 10 per cent of filler the 
resulting mixture was very mushy and marked badly on the street, 
although it showed by analysis over 19 per cent of 200-mesh material 
and consequently might be supposed to be a stable mixture. An 
increase of the filler to 12 per cent improved the general character 
of the mixture very much, but it was never satisfactory and the 
use of this sand was abandoned, although it was at first hoped that 
such a fine mixture, giving an extremely close surface, might be 
more satisfactory than the coarser standard mixture. 

On the other hand, in Toronto, Ont., and in Rochester, N. Y., 
where the sands at the same time contained 23 and 20 per cent, 
respectively, of 200-mesh material, the amount of filler could not 
be carried beyond 4 per cent, as a larger quantity made both mix- 
tures very bally and impossible to roll and rake on the street. In 
these cases the 200-mesh material apparently acted in itself largely 
as a filler. At other points loamy sands have been found the 
loam in which, when it does not bake into balls on being heated 
in the sand-drums, proves to be a satisfactory filler. 

The character of a 200-mesh material in any sand cannot be 
determined by the use of sieves, as nothing finer than the 200-mesh 
sieve is available and this will not differentiate between sand 
grains of 200-mesh size and the impalpable powder which acts 
as a filler, but this may be done by elutriating the material by 
the method described elsewhere. In the sands in use in New 
York, especially in that from Cow Bay on Long Island, consider- 
able extremely fine material is found, this amounting at times 
to 10 per cent or more passing a 200-mesh sieve. On separation 
of this material and elutriation it was found that between 50 and 
60 per cent of it would at times be in the nature of a filler and 
at others not more than 30 per cent. In a case where the pro- 
portion of sand and filler were about the same it was found that the 
mineral aggregate would still carry a very considerable further 
proportion of filler and that the grading must be regarded as 



SURFACE MIXTURES. 



347 



being extended in the fine direction as if there were a possibility 
of differentiating the material with finer sieves than are available. 
Such a mineral aggregate would carry between 11 and 12 per 
cent of bitumen, frequently approaching the latter. As will be 
seen when considering the grading of a coarse asphaltic concrete, 
in such a material the percentage of bitumen is much reduced by 
the addition of the larger particles, and it may, therefore, be 
assumed that on either side of our standard grading we may place 
other gradings according to the following scheme. It is, of course, 
to be understood that with very fine grains a certain amount of 
fine filler would be present, although theoretically absent, while 
the same would hold in regard to fine material with coarser 
mixture. 



Sieves. 




Stand. 
Mix. 






14 

13 

13 

13 

24 

11 

8 

5 

3 










10.5 

13 
13 
13 
24 
11 

8 

5 

3 












8.0 


600 


13 

13 

13 

24 

11 

8 

5 

3 




13 

13 

13 

24 

11 

8 

5 

3 




13 

13 

13 

24 

11 

8 

5 

3 




13 

13 

13 

24 

11 

8 

5 

3 




13 

13 

13 

24 

11 

8 

5 

3 




13 

13 

13 

24 

11 

8 

5 

3 




13 
13 
13 

24 
11 
8 
5 
3 





500 




400 




300 




200 




100 




80 




50 




40 

30 


13 


20. . 




13 


10. . 






13 


5. . 








24 


3 










11 


2. . 












8 


1 














5 


\ 
















3 























The above diagram shows that, theoretically, the standard 
can be pushed up and down, according to the amount of fine and 
coarse material which is present, and that at the same time it 
will be found that the amount of bitumen which the mineral 
aggregate will carry will change to a marked degree. This may 
be illustrated by the following mixtures: 



348 



THE MODERN ASPHALT PAVEMENT. 







New York, 


Chicago, 


Boston, 


Newark, 






1904. 


1901. 


1901. 


1901. 


Bitumen 


12.0% 
19.0 


11.4% 

18.6 


10.7% 
14.3 


9.6% 
9.4 


Passing 200-mesh sieve 


" 100- 
80- 


t 1 1 


io.o \ 19 

9.0/ iy 


33.0 1 47 
14.0 j 47 


12.0 \ 24 
12.0 / J4 


li.oi 17 

6.0/ 17 


50- 


(i i i 


26.0 


18.0 


26.0 


18.0 


40- 


i f i 


12.0 


2.0 


10.0 


16.0 


30- 


t <{ 


6.0] 


1.0] 


7.0] 


12.0] 


2C- 


i it 


4.0 \ 12 


1.0 I- 3 


5.0 15 


9.0 \Z0 


10- 


t it 


2.0J 
100.0 


l.oj 


3.0J 


9.0 J 




100.0 


100.0 


100.0 



ASPHALTIC 


CONCRETES. 








Barber Asphalt 
Paving Co., 
New York. 


Warren Bros., 
St. Louis, Mo. 


Bitumen 


6.2% 
7.8 
29.0 

18.0] 
21.0 ^57 
18. OJ 


3.4% * 
2.9 
12.0 


Filler 


Sand 


Stone passing \" screen. . . . 

" r u .... 

1 ' retained on 1" screen . 


4.2^ 
6.6 
55.6 
15.3. 


■81.7 


1C0.0 


100.0 





1 Coal-tar soluble in CS2. 

It is very evident from the preceding that the grading of a 
mineral aggregate has a very large bearing on the amount of bitu- 
men that it can carry, and it may be stated as a general rule that : 

1. If the sand is finer than the standard, increase the filler 
and the asphalt cement. 

2. If the sand becomes coarse, reduce the filler and the asphalt 
cement. 

3. If the 200-mesh material in the sand is high, determine 
whether it is sand or a filler. If it is a sand, and cannot be avoided 
by the use of sand from some other source, and if it acts badly 
in the mixture, get rid of it if possible by means of blowing it 
out with a forced draft or suction, or add more filler and more 
asphalt cement if this is impossible. If a portion of it is of the 
nature of a filler allow for this in the amount of filler that is 



SURFACE MIXTURES. 



349 



added. If the only available sand contains 200-mesh grains, 
which make a mushy mixture, remedy this by the addition of 
more filler if possible. In some cases the 200-mesh sand will give 
a mushy mixture under all circumstances and in this case every 
effort should be made to do away with the use of such material, 
or to remove the defect by mixing it with some other sand supply. 
Examples of the percentage of 200-mesh material which is 
so fine as to act as a filler, since it does not settle in water in 15 
seconds, is shown for the sands of various cities in the following 
table: 

ELUTRIATION OF 200-MESH MATERIAL FROM PLATFORM SAND 



Test number 

City 

Material passing 200-mesh . . . 
Acting as filler 

Test number 

City 

Material passing 200-mesh . . . 
Acting as filler 



71714 

Kansas City, 
Mo. 

3% 
17.2% 



55560 

Chicago, 

111. 

6% 

10.9% 



56372 

Toronto, 
Ont. 
23% 
8.6% 



74814 

Ottawa, 
Ont. 



13% 

27% 



73176 

Seattle, 
Wash. 



10% 
46.4% 



72355 

Buffalo, 

N. Y. 



12% 
43.2% 



73420 

Long Isl- 
and City, 

N.Y. 

18% 
54.3% 



Examples of very mushy mixtures have not been infrequent 
in the West. Some years ago a mixture was turned out in Louis- 
ville, Ky., having the following composition: 

Bitumen 11 . 7% 

200-mesh 17.3 

" 100- " 6.0i 

80- " 4.0/ 

" 50- " 39.0 

" 40- " 19.0 

" 30- " 1.0 

" 20- " 1.0 }• 

" 10- " 1.0 

100.0 



350 



THE MODERN ASPHALT PAVEMENT. 



In this mixture about 10 per cent of dust was being used before 
it was brought to the attention of the author. On examination 
it was found that the sand was deficient in 100- and 80-mesh 
grains and contained from 5 to 7 per cent of loam acting as a filler. 
The reduction of the dust to 4 per cent changed its character so 
much that it was no longer mushy. The modified surface has 
proved entirely satisfactory. 

In the early days of the industry much difficulty was met 
with, as has been mentioned in discussing the nature of sands, 
in turning out a satisfactory mixture in two western cities where 
river sands were in use. In both cases this was only overcome 
by the entire abandonment of the supplies in use and the selection 
of others. With the old supplies the mineral aggregate would 
not carry ten per cent of bitumen and the amount varied with 
different deliveries of sand. In another city the mineral aggre- 
gate, while well graded, carried too little bitumen to permit the 
finished surface from responding to the great contraction, due 
to sudden drops of temperature, with the result that all the pave- 
ments in this city were a mass of cracks. With the selection of 
other sand supplies this has been overcome, and mixtures having 
the following composition have been produced: 



Bitumen 

Passing 200-mesh 

" 100- " 

80- " . 

50- " 

40- " , 

30- " , 

20- " 

10- " 



City No. 1, 



1896. 



9.9% 

14.1 
9.0 
13.0 
33.0 
11.0 



100.0 



1904. 



11.3% 

15.7 
15.0 
14.0 
27.0 

6.0 

5.0 

4.0 

2.0 



100.0 



City No. 2, 



1896. 



9.4% 

9.6 
11.0 
18.0 
26.0 
1.1.0 

9.0 

4.0 

2.0 



100.0 



1901. 



10.6% 

11.4 
11.0 
17.0 
30.0 
10.0 

6.0 

3.0 

1.0 



100.0 



Here the difficulty lay in the fact that the sand first in use 
was composed of grains which had a surface of such a nature that a 
thick coating of asphalt cement would not adhere to them. 



SURFACE MIXTURES. 351 

The Amount of Asphalt Cement or Bitumen which a Mineral 
Aggregate Will Carry. — It has become very evident from what has 
been said in the preceding pages that the amount of bitumen or 
asphalt cement in any mixture is very variable, depending upon the 
grading of the mineral aggregate and upon the peculiar surface of 
the sand grains. It is a self-evident fact that this amount in any 
mixture should be sufficient to thickly coat every particle of mineral 
matter and fill the voids in the sand ; if the latter are sufficiently 
small, in the actual size of the spaces between the grains but not 
in volume, to permit of doing so without making the resulting 
asphalt surfaces too susceptible to temperature changes. With 
too much bitumen the sand grains composing the mineral aggregate 
are readily displaced among themselves, especially in the absence 
of a sufficient amount of filler, and the surface is not stable and 
will mark badly and push out of shape. With too little bitumen 
the surface cracks, owing to its inability to withstand sudden 
changes in temperature, and also becomes displaced because it is 
not a solid mass. Mr. Dow's illustration, which compares an asphalt 
pavement to a seabeach at different states of the tide, is an excellent 
one. Beach sand with the voids just filled with water, as the 
tide goes out, is firm and stable. A horse hardly marks it. When 
it begins to dry out it is loose and is readily displaced. When it is 
supersaturated with water it is a quicksand. 

The proper amount of bitumen for various mineral aggregates 
in common use may vary from 9 to over 14 per cent. As examples 
sands found and in use in Moline, 111., in 1902, would carry but 8.5 
per cent of bitumen, while in Paris, France, and London, England, 
11.5 per cent could be used, and in Glasgow, Scotland, and Seattle, 
Wash., over 12.5 per cent, as shown by the following analyses. See 
table on page 352. 

If a strict interpretation of the instructions is followed and only 
10.5 per cent of bitumen is introduced the mixture with such sand 
will, of course, be unsatisfactory, and such difficulties have been 
frequently met with owing to lack of judgment on the part of 
yard foremen and superintendents. 

The actual amount to be used in any case must be determined 
by the pat-paper test described on page 514. This test, however, 



352 



THE MODERN ASPHALT PAVEMENT. 



is deceptive unless the mixture is at a temperature where the asphalt 
cement is quite liquid. With cold mixtures the test is of no value, 
while excessively hot ones may stain the paper too freely. 



City 

Bitumen soluble in CS 2 

Passing 200-mesh sieve 

100- " 

" 80- " " 

" 50- " 

« 30 _ n a 

it 20- " " 

« 1Q . a a 



Moline 


Paris 


London 


Glasgow 


8.4% 


11.2% 


11.1% 


12.0% 


15.6 


14.7 


15.3 


18.0 


14.0 


18.7 


12.7 


15.0 


4.0 


23.1 


20.5 


25.0 


16.0 


26.3 


33.7 


24.0 


17.0 


3.9 


3.6 


4.0 


13.0 


1.6 


1.5 


2.0 


9.0 


.4 


1.1 


0.0 


3.0 

100.0 


.1 

100.0 


.5 


0.0 
100.0 


100.0 



Seattle 

12.3% 

12.7 

11.0 

9.0 
23.0 
15.0 
10.0 

5.0 

2.0 



100.0 



Characteristic pat papers are illustrated on the following sheets. 

The paper, Fig. 6, illustrates a light stain made by a mixture 
which, although of a proper temperature, is deficient in bitumen. 
The paper reproduced in Fig. 7 illustrates a medium stain, 
showing a slight deficiency in bitumen. The paper reproduced 
in Fig. 8 shows a strong stain produced by a standard mixture 
carrying a suitable amount of bitumen. The paper reproduced 
in Fig. 9 represents a heavy stain, pointing to the presence of 
an excess of bitumen if the temperature of the latter is not abnor* 
mally high. 

Coarse sands such as are found in abnormal mineral aggregates 
give a rather different stain. Experience will prove the best 
means of interpreting the test. It is a very valuable one with 
Trinidad lake asphalt mixture, but less so with others, as other 
bitumens are more susceptible to temperature changes. 

In making a pat test the appearance of the surface of the ho<i 
pat is quite as instructive as that of the stain upon the paper, 
since if the mixture is unbalanced in any way greasiness is often 
visible, which should be removed by the adjustment of sand, filler, 
and bitumen, which can only be accomplished by experiment, 
the reduction of the amount of filler accomplishing this at one 
time and increasing it at another. 



infrv.i,^, -..;.'. 










Fig. 6. — Light Stain. 



353 



Fig. 7. — Medium Stain. 



354 




Fig. 8. — Strong Stain. 



355 




Fig. 9. — Heavy Stain. 



356 



SURFACE MIXTURES. 



357 



Reasons for the Necessity for a Larger Percentage of Bitumen 
in a Fine than in a Coarse Mixture. — It has already been mentioned 
that one reason why the finer mixture requires a larger percentage 
of bitumen than the coarser one is that the extent of surface of 
the sand grains to be covered with bitumen is much larger in the 
former than in the latter case. 

The number of particles in a gram of grains of uniform diameter 
and of different sizes and the square centimeters of surface exposed 
by one gram of such grains are presented in the following tables. 

These figures are obtained by means of the following formulas: 



7r(d)*co 



= n 



6 



and 



surface = n(d) 2 n, 



where a is the weight of the particles, in this case one gram, d the 
diameter of the particles, a> the specific gravity of them, and where 
n is the number of particles. 

Where the diameter, d, is given in centimeters and a in grams, 
the following constants are useful: 



LOGARITHMS OF CONSTANTS IN CENTIMETERS. 



Mesh Sieve. 


Centimeters. 


. n(d) 3 ai 
log 6 . 


log n(d) 2 n. 


10 


.150 


6.6705180 


8 . 8493321 


20 


.084 


6.9150320 


8.3457081 


30 


.058 


6.4325281 


8.0240055 


40 


.040 


5 . 9484241 


7.7012695 


50 


.026 


5.3871640 


7.3270961 


80 


.020 


5.0453441 


7.0992095 


100 


.013 


4.4840743 


6.7250363 


200 


.008 


3.6515141 


6,3033295 


1 minute 


.005 


3.2491541 


5 . 8949895 


30 minutes 


.0025 


2.3330641 


5.2930295 


2 hours 


.00075 


. 7674280 


4.2472721 


16 " 


.00025 


0.3350641 


3.2930295 



log ~ = . 1422441. 



358 



THE MODERN ASPHALT PAVEMENT. 



ONE GRAM OF SAND OF UNIFORM SIZE CONTAINS. 



Mesh Sieve. 


Millimeter. 


Particles. 


Square 
Centimeters. 


10 


1.50 


212.8 


15.0 


20 


.84 


1,215.9 


27.0 


30 


.58 


3,693.6 


39.4 


40 


.40 


11,261.0 


56.6 


50 


.26 


41,005.0 


87.1 


80 


.20 


90,066.0 


113.2 


100 


.13 


328,032.0 


174.2 


200 


.08 


1,407,620.0 


283.0 


1 minute 


.05 


5,643,700.0 


442.4 


30 minutes 


.025 


46,124,900.0 


905.7 


2 hours 


.0075 


6,800,990,000.0 


1,201.6 


16 " 


.0025 


46,124,900,000.0 


9.056.6 



1 gram to 1 lb. X 453.59, log. 2.6566654 for particles. 
Sq. cm. to sq. ft., divide by 2.9680569 for surface. 

Where it is desired to determine the number of particles and 
the surface exposed by grains of different sizes which go to make 
up an aggregate of definite weight, the preceding formulas become: 



7l(d) 3 CO ' A ' 



where a is the weight of each group of particles and A the total 
weight of the material, in the following case one pound. Using 
this, the number of particles and the square feet of surface in one 
pound of the mineral aggregates in New York mixtures of 1895 
and 1898 are found to be as follows. See tables on page 359. 

It appears that the finer aggregate presents a surface of 
60.5 square feet to the pound, the coarser only 44.4, or 39,407 and 
52,093 square feet per 9 cubic foot box respectively; that is to 
say, the finer has one-third more surface, and as this must be covered, 
more asphalt will be required for the finer than the coarse aggre- 
gate. This explains why the addition of dust will always increase 
the amount of asphalt cement which a mixture will hold, although 
the voids may be reduced, as a pound of the best Long Island 



SURFACE MIXTURES. 



359 



NUMBER OF PARTICLES AND THEIR SQUARE FEET OP 

SURFACE IN ONE POUND OF SAND AND DUST. 

New York Mixture, 1895. 



Mesh Sieve. 


Per Cent. 


Particles. 


Square Feet 
of Surface. 


10 


13 


12,592 


.958 


20 


12 


66,186 


1.579 


30 


10 


167,547 


1.901 


40 


13 


664,250 


3.593 


50 


27 


5,021,870 


11.479 


80 


10 


4,086,220 


5 . 527 


100 


7 


10,415,700 


5.952 


200 


5 


31,924,300 


6.909 


.005 mm. 


3 
100 


76,671,400 


6.480 


129,030,065 


44.378 



One box of mixture (average 888 lbs.), 39,407.664 
New York Mixture, 1898. 



10 


4 


3,674 


.295 


20 


7 


38,808 , 


.921 


30 


9 


150,796 


1.715 


40 


11 


561,866 


3.033 


50 


26 


4,835,870 


11.054 


80 


15 


6,127,910 


8.099 


100 


15 


22,319,400 


12 . 754 


200 


7 


44,694,000 


9.672 


.005 mm. 


6 
100 


153,343,000 


12.960 


232,075,324 


60 . 503 



One box of mixture (average 861 lbs.), 52,093.083 
City dust with the following siftings will contain the number- of 
particles and the surface in square feet given below : 



Size Particles, 
Centimeters. 


Per Cent. 


Number of Particles. 


Square Feet 

of 

Surface. 


.008 

.005 

.0025 

.00075 

.00025 

or if all of t 
.0025 cm. 


18.8 

17.7 
51.3 

5.0 

7.2 


120,035,300 

452,3^0,200 

10,732,9^0,000 

30,775,730,000 

150,634,400,000 

192,715,475,500 
20,922,050,000 


25.976 
38.231 

226.825 
58 . 590 

178.199 


100.0 

tie dust is of 
n diameter: 


527.821 
442.157 



360 THE MODERN ASPHALT PAVEMENT. 

This enormous area of surface allows the presence of a larger 
quantity of bitumen in a fine mixture than in a coarse one. The 
question of the thickness of the film of the melted asphalt cement 
on the extended surface of the sand grains is one which, from 
the elaborate studies of soil physics, it is plain must be of great 
importance in regulating the amount of bitumen which different 
sands will require to prevent porosity and instabilty in the mix- 
ture. Much pertinent information on this point will be found 
in Whitney's Bulletins, Weather Bureau, Division of Soils, U. S. 
Department of Agriculture, and Wiley's Principles of Agricultural 
Analysis, but our understanding of the question at present is 
insufficient to permit of going into the matter at this time. It 
will be investigated in the future. 

In this connection some recent determinations by Messrs. 
Briggs and McCall, of the Bureau of Soils, U. S. Department of Agri- 
culture, " On the Thickness of Adsorbed Aqueous Films," are of 
interest. They found the following values for several materials : 

Silica 167.00X10- 6 cm. 

Glass 18.00X10- 8 " 

Quartz 45X10~ 6 " 

The application of these data to an asphalt surface lies in 
the fact that' sand may consist of particles which may vary as 
largely in the thickness of the film of asphalt which will adhere 
to them as the materials experimented with above, and this may 
explain why one sand with the same grading and voids as another 
may hold different percentages of bitumen. 

The New York mixture is desirable in so far as it will usually 
carry 10.5 to 11.5 per cent of bitumen, when the grains are all 
coated and the voids filled, as shown by the paper pat test, and 
this affords a sufficient amount to keep out water and provide 
for the contraction due to a rapid fall in temperature. 

With the low voids it might at first be assumed that such a mix- 
ture would hold less asphalt than one with a greater volume, but 
it has already been shown that the low voids, when accompanied 
by plenty of fine sand, do not have this effect, as the adsorbed 
bitumen, or that necessary as a paint coat to cover the more numer- 



SURFACE MIXTURES. 



361 



cms small grains, is something to be considered beyond that necessary 
to fill the voids. On the contrary, a well-graded fine mixture 
with small voids will often carry more bitumen than a coarse 
one with larger voids. 

Comparison of the Characteristics of Different Sands Having 
the Same Sand Grading. — If the sand used in New York, arranged 
according to the grading in the mixture laid in that city in 1898 
and 1899, is to be regarded as most satisfactory, as shown in the 
following figures, it must be by no means assumed that on 
that account the New York sand is the best sand; that is to 
say, consists of the best shaped grains or of those having the 
best surface to afford a proper adhesion of the asphalt cement 
and allow of a sufficiently thick coating. As a matter of fact 
the contrary is the case. It is possible that with other sands 
accommodated to the New York grading even better results could 
be obtained than with the New York sands themselves. 



Bitumen. . . . 

Passing 200-mesh sieve. . .. 

100- ' 

80- 

50- 

" 40- 

30- 

20- 

10- 



1898. 



10.5% 

13.7 

13.1 

13.4 

22.6 

10.0 

7.6 

5.6 

3.5 



100.0 



1899. 



10.5% 

13.0 

12.7 

12.6 

23.9 

12.1 

6.6 

5.3 

3.3 



100.0 



Experiments have been undertaken and completed for determin- 
ing what the differences are in this respect in the available sands 
in different cities of the country. 

It has been shown that the grading of the New York mineral 
aggregate is such that the New York mixture is the densest of any 
satisfactory one in the country, and it appears that in the case of 
the sand of every other city in the country, when the grading 
according to which it was used some years ago is changed to that 
of the New York mineral aggregate of to-day (1899), the density 



362 



/HE MODERN ASPHALT PAVEMENT 



of the resulting mixture is increased with one or two exceptions, 
and in the same way if the New York aggregate is changed from 
its own grading to those of other cities its density is decreased. 

The grading of the local sands with and without dust, the voids 
and the weight per cubic foot of each on its own grading, on the 
grading of the New York sand and aggregate and of the New York 
sand on the local grading as determined in 1900 are given in the 
following tables: 
GRADING OF SANDS IN AVERAGE MIXTURES IN DIFFERENT 

CITIES WITH 200-MESH MATERIAL REMOVED— 1898 AND 

1899. 





Passing Mesh. 


Year. 




100 


80 


50 


40 


30 


20 


10 




Philadelphia, Pa.. 

Chicago, 111 

Kansas City, Mo. . 
New York, N. Y.. 

Omaha, Neb 

St. Louis, Mo ... . 
Boston, Mass. .... 
Paterson, N. J. . . 
Trenton, N. J. ... 
Washington, D. C. 
Louisville, Ky. .. . 
Youngstown, 0. . 


22 
21 
17 
17 
17 
16 
16 
15 
11 
10 
10 
7 


18 

17 

19 

17 

16 

14 

12 

13 

14 

7 

6 

7 


30 
44 
37 
30 
34 
38 
30 
35 
25 
23 
50 
23 


14 
10 
10 
13 
15 
15 
19 
17 
14 
26 
26 
26 


7 

4 

8 

10 

8 

7 

10 

10 

12 

13 

4 

13 


5 
3 
5 

8 

6 

6 

8 

6 

13 

11 

2 

11 


4 

1 

4 

5 

4 

4 

5 

4 

11 

10 

2 

10 


1899 

1898 
1898 
1898 
1899 
1899 
1899 

1898 

1899 

1898 



GRADING OF SANDS 
CITIES WITH 


IN AVERAGE MIXTURES IN DIFFERENT 
13 PER CENT OF 200-MESH DUST. 




Passing Mesh. 


Year. 




200 


100 


80 


50 


40 


30 


20 


10 


Philadelphia, Pa. . . 

Chicago, 111 

Kansas City, Mo. . 
New York, N. Y . . 

Omaha, Neb 

St. Louis, Mo 

Boston, Mass 

Paterson, N. J. . . . 
Trenton, N. J. . ... 
Washington, D. C. . 

Louisville, Ky 

Youngstown, O. . . 


13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 


15 

18 

15 

15 

15 

14 

14 

13 

10 

9 

9 

6 


15 
15 
16 
15 
14 
12 
10 
11 
12 
6 
5 
16 


26 
38 
32 
26 
30 
33 
26 
31 
22 
20 
44 
31 


11 

9 
9 
11 
13 
13 
17 
15 
12 
23 
23 
14 


9 

3 

7 

9 

7 

6 

9 

9 

10 

11 

3 

13 


7 
3 
4 
7 
5 
5 
7 
5 
11 
9 
2 
6 


4 
1 
4 
4 
3 
4 
4 
3 
10 
9 
1 
1 


1898 
1898 
1898 
1898 
1899 
1899 
1899 
1898 
1898 
1899 
1899 
1898 



SURFACE MIXTURES 



363 



WEIGHT PER CUBIC FOOT AND VOIDS IN NEW YORK SAND. 
WITH NO 200-MESH SAND AND WITH 13 PER CENT DUST, 
MADE UP ON THE GRADING OF VARIOUS CITIES, COM- 
PARED WITH THE SAND FROM THESE CITIES OF THE 
SAME GRADING AND WITH THAT OF THE CITIES MADE 
UP ON THE NEW YORK GRADING. 



New York 

Omaha, local grading 

Omaha, N. Y. " 

N. Y., Om^ha " 

Trenton, local grading 

Trenton, N. Y. " 

N. Y., Trenton " 

Kansas City, local grading. . . 
Kansas City, N. Y. " .... 
N. Y, Kansas City " ... 

St. Louis, local grading 

St. Louis, N. Y. " 

N. Y, St. Louis "■ 

Paterson, local grading 

Paterson, N. Y. " 

N. Y, Paterson " 

Buffalo, local grading 

Buffalo, N. Y. " 

N. Y, Buffalo " 

Chicago, local grading 

Chicago, N. Y. " 

N. Y, Chicago " 

Philadelphia local grading. . . 
Philadelphia, N. Y. " ... 
N.Y, Philadelphia " ... 

"V\ ashington, local grading. . . 
Washington, N. Y." " 
N. Y, Washington " 

Louisville, local grading 

Louisville, N. Y. " 

N. Y , Louisville " 



Specific 
Grav- 
ity. 


With no 200. 


With 13 Per Cent 
Dust. 


Weight 

per Cubic 

Foot. 


Voids. 


Weight 

per Cubic 

Foot. 


Voids. 


2.67 


109.6 


34.1 


118.9 


28.5 


2.63 


113.3 


30.9 


124.5 


24.0 




114.1 


30.3 


126.0 


23.1 




110.0 


33.3 


121.4 


27.2 


2.61 


111.1 


31.6 


123.5 


24.1 




109.0 


32.6 


118.6 


26.9 




113.7 


31.7 


125.6 


24.5 


2.63 


110.4 


32.6 


122.4 


25.3 




111.8 


31.8 


124.0 


24.3 




110.3 


33.7 


121.9 


26.7 


2.63 


111.9 


31.7 


122.2 


25.4 




113.8 


31.9 


124.0 


25.7 




109.7 


34.1 


121.1 


27.1 


2.63 


110.6 


32.6 


121.0 


26.2 




110.0 


32.9 


122.2 


25.4 




110.6 


33.5 


121.4 


27.1 


2.66 


109.6 


33.9 


120.5 


27.3 




111.8 


32.4 


124.2 


25.0 




106.8 


35.8 


118.8 


28.6 


2.68 


109.1 


34.6 


120.4 


27.9 




112.5 


32.6 


123.2 


26.2 




107.8 


35.1 


119.1 


28.1 


2.67 


107.8 


35.2 


119.4 


28.2 




109.6 


34.1 


121.7 


26.8 




110.3 


33.7 


121.5 


27.0 


2.66 


106.1 


36.5 


119.0 


26 8 




107.2 


34.3 


117.3 


26.2 




112.4 


32.4 


124.0 


25.5 


2.62 


104.5 


36.0 


115.7 


29.1 




107.2 


34.3 


117.3 


28.2 




108.6 


34.7 


120.4 


27.6 



364 



THE MODERN ASPHALT PAVEMENT. 



In the preceding determinations of voids in different local 
sands the sands have been freed from all 200-mesh grains before 
adding the filler. In practice these sands always contain from 
1 per cent of this material in Chicago to 13 per cent in Buffalo. 
Where so much 200-mesh material not dust is present the full 
amount of filler cannot always be used. The actual average 
amount of 200-mesh sand in the supplies of the special cities, 
which have been examined, and that of the filler used in 1899, 
with the percentage of the latter passing a 200-mesh sieve, is 
given in the following table : 

AVERAGE PER CENT OF SAND PASSING 200-MESH TAKEN 
FROM WEEKLY REPORTS; ALSO PER CENT USED IN 
MIXTURE. 



City. 



New York. . 
Chicago. . . . 
St. Louis. . . 
Louisville. . . 
Kansas City. 

Omaha 

Trenton. . . . 
Paterson. . . 
Youngstown 
Washington. 

Boston 

Buffalo 



Year. 


Average 

Per Ceat 

Passing 

200-Mesh. 


Average 
Per Ceat 
Dust in 
Mixture. 


Per Cent 

Dust 

Passing 

200-Mesh. 


Per Cent 
200 Dust 
Added. 


1898 


5.0 


8.0 


95.0 


7.6 


1898 


1.0 


10.0 


85.0 


8.5 


1899 


7.0 


5.0 


70.0 


3.5 


1899 


10.0 


8.0 


70.0 


5.6 


1898 


6.0 


10.0 


70.0 


7.0 


1899 


4.0 


8.0 


CO.O 


4.8 


1898 


2.0 


7.0 






1899 


6.0 


6.0 


COO 


3.6 


1898 


1.0 


11.0 


70.0 


7.7 


1899 


11.0 


8.0 


65.0 


5.2 


1899 


8.0 


7.0 






1899 


13.0 


5.0 


eo.o 


3.0 



Total 
200 Sand 
and Dust. 



12.6 
9.5 
10.5 
15.6 
13.0 
8.8 

9.6 

8.7 

16.2 

16.0 



In Buffalo, with 13 per cent of 200 sand, only 3 per cent of 
filler can be used, while in Chicago, with only 1 per cent, 8.5 per 
cent or more is used. The total per cent of 200-mesh sand and 
dust in many cases is below the amount which should be found 
in a good mineral aggregate, but it must be remembered that 
nearly 3 per cent of 200-mesh filler is contributed to the mixture 
by the fine mineral matter where a Trinidad asphalt cement is 
in use. Where Bermudez asphalt is the cementing material an 
additional amount of filler is of course required. 



SURFACE MIXTURES. 



365 



If all these sands are taken and enough dust added to make 
the total 200-mesh material in the aggregate up to 15 per cent 
the voids in these aggregates can be determined and the influence 
of the presence of the 200-mesh sand investigated. This has 
been done and the results follow: 



WEIGHT PER CUBIC FOOT AND VOIDS IN THE AVERAGE 
SAND OF 1899 FROM VARIOUS CITIES, WITH THE AVERAGE 
AMOUNT OF 200-MESH SAND AND ENOUGH FILLER ADDED 
TO BRING IT UP TO 15 PER CENT, PASSING 200-MESH, AND 
WITH 200-MESH SAND REMOVED AND REPLACED BY FILLER. 



City. 



Average 
200 Sand. 



Amount 

Dust 
Added. 



Weight per Cu Ft. 



Without 

200-Mesh 

Sand. 



With 

200-Mesh 

Sand. 



Voids. 



Without 

200-Mesh 

Sand. 



With 

200-Mesh 

Sand. 



New York. . 
Chicago. . . . 
St. Louis. . . 
Louisville. . . 
Kansas City. 

Omaha 

Trenton. . . . 
Paterson. . . 
Washington. 

Buffalo 

Philadelphia 



5.0 
1.0 

7.0 
10.0* 
6.0 
4.0 
2.0 





ot 






10.0 

14.0 

8.0 

5.0 

9.0 

11.0 

13.0 

9.0 

4.0 

2.0 

11.0 



118.9 
120.4 
122.2 
115.7 
122.4 
124.5 
123.5 
121.0 
119.0 
120.5 
119.5 



120.4 
120.7 
121.1 
114.5 
121.4 
125.3 
125.2 
121.2 
117.4 
117.0 
120.9 



28.5 
27.9 
25.4 
29.1 
25.3 
24.0 
24.1 
26.2 
28.8 
27.3 
28.2 



27.6 
27.7 
25.8 
30.0 
26.0 
23.6 
23.0 
26.0 
28.4 
29.4 
27.3 



* Largely fine loam acting as a filler. 

t Largely crushed-stone dust acting as a filler. 



With only 1 per cent of 200 sand, as in Chicago, little difference 
is occasioned, but in Buffalo, with 13 per cent of 200 sand, the voids 
are greater with the sand than with this taken out and substi- 
tuted by filler. Where the 200-mesh material in the sand is more 
of the nature of filler than sand there is little difference, but if 
the 200-mesh material is really sand of the largest size which will 
pass a 200 sieve the difference is striking. The substitution of 
such a sand for filler has been made with the sands from the several 
cities and the results show the effect when compared with those 
obtained with filler on a previous page : 



366 THE MODERN ASPHALT PA YEMEN r 

EFFECT OF SUBSTITUTION OF SAND FOR FILLER. 



New York 

Omaha, local grading 

Omaha, N. Y. " 

N.Y., Omaha " 

Trenton, local grading. . . . 
Trenton, N. Y. " 
N.Y., Trenton " .... 

Kansas City, local grading, 
Kansas City, N. Y. " . 
N. Y., Kansas City " . 

St. Louis, local grading. . . 
St. Louis, N. Y. " ... 
N. Y., St. Louis " ... 

Paterson, local grading 

Paterson, N. Y. " .... 
N. Y., Paterson " .... 

Buffalo, local grading 

Buffalo, N. Y. " 

N.Y., Buffalo " 

Chicago, local grading. . . . 

Chicago, N..Y. " 

N.Y., Chicago " 

Philadelphia, local grading 
Philadelphia, N. Y. " 
N. Y., Philadelphia " , 

Washington, local grading. 
Washington, N. Y. " . 
N. Y., Washington " . 

Louisville, local grading. . . 
Louisville, N. Y. " ... 
N. Y., Louisville " ... 



13 Per Cent. 200-Mesh Sand. 



Weight per 
Cubic Foot. 


Voids. 


115.6 


30.5 


118.6 
118.9 
118.0 


27.6 
27.4 
29.1 


117.1 
114.6 
120.0 


28.2 
29.5 
27.8 


115.0 
116.8 
117.0 


29.9 

28.8 
29.7 


. 116.1 
117.1 

118.2 


29.1 
29.9 
28.9 


115.6 
116.9 
118.2 


29.6 
28.6 
29.0 


115.9 
118.4 
114.8 


30.1 

28.4 
31.0 


113.0 
117.6 
115.1 


32.3 

29.6 
30.8 


113.3 

112.7 
117.0 


33.1 
32.3 
29.7 


114.8 
112.3 
120.2 


31.4 
32.8 
27.8 


110.9 
112.8 
117.3 


32.1 
30.9 
29.5 



200-mesh sand is generally undesirable because it tends to 
make the mixture less stable and liable to move, as has already 
been shown. Our ideal mixture should, therefore, as a rule con- 



SURFACE MIXTURES. 367 

tain none of this material, and in this respect the New York mix- 
ture is at times capable of some improvement, although at others, 
with quite large amounts, an extremely satisfactory result is 
obtained. 

It is evident from the preceding facts that something besides 
the mere grading of the sand has large influence on the character 
of the mineral aggregate and the asphalt surface mixture pre- 
pared from it, and this can probably be explained by consider- 
ation of the fact that the shape of the sand grains which are of 
size to pass any given sieve may be so entirely different that they 
fit together with different degrees of compactness, while the power 
of adsorption l of the surface of the sand grains will have an equal 
influence. This is not astonishing from what has been observed 
in regard to the character of various sand supplies when the 
subject of sand was under consideration. 

Further Characteristics Indicative of the Properties of Old 
and New Asphalt Surfaces. — In addition to the consideration of 
the preceding characteristics in judging a surface mixture, cer- 
tain of its physical properties or those of old surfaces, if one of 
these is under examination, must be determined, such as its density 
and capacity for absorbing moisture, while others may throw 
some light on the nature of old surfaces, more especially such as 
their tensile, crushing, and shearing strength. Old surfaces can 
also be reheated and the general appearance of the mixture in 
this condition noted, including the surface of a pat and the stain 
on a pat paper 2 made, at carefully regulated temperatures, as 
with a new mixture. 

Density. — The density of the best mixtures when thoroughly 
compacted either by traffic or in the laboratory, as illustrated 
by that turned out in New York at the present time, should be 
about 2.22 to 2.25 when made with ordinary limestone and 2.27 
when made with Portland cement. The density of such a mix- 
ture calculated from that of their constituents is about 2.27 and 
2.29, so that in this mixture but a small volume of voids is found. 
A comparison with these figures of the actual density of old 
street surfaces which have been examined is therefore of value. 
1 See page 360. 2 See pages 353 to 356. 



368 



THE MODERN ASPHALT PAVEMENT. 



i In the old surfaces as they exist in the streets of many cities 
of the country densities of from 1.89 to 2.26 were found. That 
on Dodge Street in Omaha had the latter density, and two good 
surfaces, one from Warwick Boulevard in Kansas City, laid in 

1892, and one from Cumming Street in Omaha, laid in 1893, 
had a density of 2.24. These densities are nearly theoretical, and 
such surfaces should be able to keep out the water. Howard 
Street in Omaha, laid in 1895, has a density of only 1.89, and Ohio 
Street in Chicago, laid in 1894 by the Standard Company, has a 
density of 2.04. Both of these pavements are cracked, the former 
very badly. Attempts to compress the latter mixture in the 
laboratory resulted in obtaining a no greater density. 

It is not always the case, however, that a surface of high density 
does not crack or the reverse. In Omaha, Dodge Street, laid in 

1893, has a density of 2.26, but it has cracked probably because 
the bitumen was too hard. In Chicago, Tripp Avenue, with a 
density of 2.21, has cracked, as has Walrond Avenue in Kansas 
City, with 2.24, for the same reason. Baltimore Avenue in Kansas 
City, of a density of only 2.11, has not cracked, nor has Thirty-ninth 
Street in Omaha, with a density of 2.10. The extreme densities 
of the surfaces examined in Chicago, Omaha, and Kansas City 
were: 





Chicago. 


Omaha. 


Kansas City. 


Good surfaces: 








High density 


2.20 


2.24 


2.24 


Low ' ' 


2.16 


2.10 


2.11 


Medium surfaces: 








High density 


.... 


2.26 




Low " 




2.09 




Cracked surfaces: 








High density 


2.15 


2.21 


2.15 


Low " 


2.04 


1.89 


2.13 



It seemed possible that a low density might be due to lack of 
compression in surfaces laid in winter. The average density of 
the summer surfaces as compared with those laid after Novem- 
ber first in Kansas City and Chicago seems to confirm this idea, 



SURFACE MIXTURES. 



369 



but in Omaha the density is slightly in favor of the one winter 
surface examined. 





Summer 

Pavements, 

Density. 


Winter 

Pavements, 

Density. 


Kansas City, Mo. 




Cracked pavements 1 2 . 235 (1) * 

Good " 1 2.201(3) 


2.145(3) 
2.136(2) 


Chicago, III. 


^ 


Cracked pavements 1 2 . 155 (5) 

Good " ...... .| 2.183(2) 


2.080 (1) 


Omaha, Neb. 




Badly cracked pavements. 
Medium good ' ' 
Good 


2 . 180 (2) 
2.170 (9) 


2.182(1) 
2.184(2) 



1 Number of surfaces examined. 



It must be remembered, however, that variations in the rela- 
tions of bitumen to sand may make a marked difference in the 
densities, since the greater the percentage of bitumen in a mixture 
the lower will be its volume weight; that is to say, an excess of 
bitumen added to an aggregate will lower the density as much 
as a deficiency. The density of the densest mineral aggregate 
before the addition of bitumen has been found to be 2.00 in Omaha, 
the lowest 1.86 in Louisville. It would not be expected, there- 
fore, that a mixture having low voids would have the same gravity 
in Louisville as in Omaha. 

Capacity for Absorbing Water. — Surfaces will absorb water 
in amount varying with the density and the percentage of bitu- 
men which they contain. With the New York mixture the amount 
of water absorbed by it in milligrams per square inch and in pounds 
per square yard when a thoroughly compacted cylinder of the 
above density is immersed in it for various lengths of time is as 
follows. See table on page 370. 

It appears that more water is absorbed in the first day's immer- 
sion than in any subsequent day and that it diminishes in a good 
mixture as time goes on. When the New York mixture is made 
with bitumens of different origin the amount of water absorbed 



370 



THE MODERN ASPHALT PAVEMENT 



WATER ABSORBED BY CYLINDER OF NEW YORK TRINIDAD 
LAKE ASPHALT MIXTURE, DENSITY 2.24, WHEN IM- 
MERSED FOR DIFFERENT PERIODS. 



Time. 


Milligrams per 
Square Inch. 


Total. 


Pounds per 
Square Yard. 


Total. 


1 day 


.0169 
.0321 
.0092 
.0045 
.0035 


!6i9o 

.0282 
.0327 
.03G2 


.0480 
.COCO 
.0203 
.0127 
.0101 




2 days 


.0540 


7 " 


.0803 


15 " 


.0930 


28 ' ' 


.1031 







will vary. This is illustrated by some data, 1 wherein it is seen 
that Trinidad asphalt-surface mixtures are quite as impervious 
as those made with other asphalts and after a lengthy exposure 
in running water are able to resist impact better than any others. 

Comparison of Sireet Surfaces with New York Mixture. — A 
comparison of the absorption of water by some of the typical 
surfaces from old streets in the western cities with that absorbed 
by the New York mixture will be of interest. See results tabulated 
on pages 371 and 372. 

These results show that the absorption in the old-time, poorly 
graded surfaces is in inverse proportion to the amount of bitumen 
they contain and that those of high density, unless they contain 
enough bitumen to fill the voids, as shown by a paper test, gain 
more than less dense mixtures with sufficient bitumen. 

Such a surface as that on Thirty-ninth Street, Omaha, which 
the pat paper shows is excessively rich in asphalt cement, excludes 
water better than the New York mixture, as does the rich War- 
wick Boulevard surface from Kansas City. The old Howard 
Street surface with less than 8 per cent of bitumen, of course, 
absorbs more water than any of the others which were examined. 
The peculiarities of the other surfaces appear from an inspection 
of the results in the table. Twenty-sixth Street in Omaha, although 
it has cracked some, absorbs a comparatively small amount of 
water, but it must be remembered that water absorption results 
more in disintegration, scaling, and rotting than in cracking. 

1 See page 468. 



SURFACE MIXTURES. 



371 



WATER ABSORBED BY CYLINDERS OF OLD SURFACE. 



Test No. 



Street. 



Density of 

Compacted 

Cylinder. 



Stain on Pat Paper. 



21440 
21442 

21445 
21446 
21447 



2144S 
21453 
214G1 
23253 
23251 
23253 
23257 



21431 
21433 
21435 
21438 



New York Mixture. 



Fifth Ave. mixture 



2.24 



Kansas City, Mo. 



Baltimore Ave. — good. . 
Garfield Ave. — cracked. 
Walrond Ave. — cracked. 
Warwick Blvd. — good. . 
Seventh — good 



Omaha, Neb. 



23d — cracked 

20th — medium good. . . 

39th— good 

Cumming — good. 

2Gth — cracked 

Capitol — medium good. 
Howard — cracked 



Chicago, III. 



Prairie — good ... ... 

Tripp — cracked. . . „ 
So. Park Ave. — cracked. 
Washington Blvd — good. 



2.240 
2.158 
2.195 

2.274 
2.248 



2.231 
2.193 
2.156 
2.201 



Heavy 



Heavy- 
Very light 
Heavy 
Very heavy, coarse 
Medium 



2.142 


Strong 


2.205 


Medium 


2.209 


Very heavy 


2.235 


Medium 


2.217 


( ( 


2.210 


Heavy 


1.904 


None 



Heavy 

Strong 

Strong 

Medium 



Why the Standard Mixture is Satisfactory. — The standard 
mixture which has been suggested by the author and which is 
now universally laid under his supervision where this is possible, 
on streets of heavy traffic and elsewhere, has been arrived at by 
the examination of surfaces which have proved successful and 
not by any theoretical reasoning or experimenting. Practice 
during the last eleven years has shown that such a mixture is 
successful. The results of laboratory investigations on the sub- 
ject have, however, made it possible to explain theoretically and 
with a good deal of satisfaction why the standard mixture has 
been a satisfactory one. The greatest factors in the construction 



372 



THE MODERN ASPHALT PAVEMENT 



WATER ABSORBED BY CYLINDERS OF OLD SURFACE. 

Absorption, Pounds per Square Yard. 



Test No. 



1 Day. 



2 Days. 



Add. Total 



7 Days. 



Add. Total. 



15 Days. 



Add. Total. 



28 Days. 



Add. Total 



21440 
21442 
21445 
21446 
21447 



21448 
21456 
21461 
23253 
23254 
23256 
23257 



New York Mixtures. 
.0480| .0060| .0540| .0263| .0803| .0127| .0930| 

Kansas City, Mo. 



.089 


.029 


.125 


.113 


.238 


.096 


.334 


.146 


.141 


.063 


.204 


.342 


.546 


.354 


.900 


.379 


.095 


.080 


.175 


.231 


.406 


.357 


.763 


.530 


.050 


.017 


.067 


.068 


.134 


.074 


.208 


.119 


.115 


.065 


.181 


.319 


.499 


.286 


.785 


.434 J 







Omaha, 


Neb. 








.128 


.051 


.178 


.292 


.469 


.426 


.896 


.693 


.106 


.060 


.166 


.234 


.399 


.185 


.585 


.267 


.032 


.012 


.045 


.052 


.097 


.046 


.142 


.091 


.062 


.027 


.089 


.125 


.215 


.146 


.361 


.210 


.068 


.025 


.093 


.118 


.211 


.133 


.344 


.226 


.066 


.043 


.109 


.415 


.524 








.273 


.103 


.376 


.531 


.907 


.767 


1.674 


.505 



0101| .1031 



.480 
1.279 
1.343 

.327 
1.219 



1.589 
.852 
.234 
.571 
.570 



2.259 



Chicago, III. 



21431 


.058 


.017 


.075 


.069 


.144 


.073 


.217 


.103 


.319 


21433 


.096 


.043 


.139 


.221 


.360 


.282 


.642 


.386 


1.028 


21435 


.106 


.053 


.159 


.291 


.450 


.338 


.787 


.473 


1.253 


21438 


.089 


.037 


.126 


.208 


.334 


.241 


.575 


.309 


.884 



of a successful asphalt surface is that the mixture shall be so 
dense as to resist the action of water and impact and at the same 
time contain sufficient bitumen to permit its responding, without 
cracking, to a sudden fall in temperature. The standard mixture 
seems to offer these advantages in a way not supplied by a coarser 
and more carelessly prepared mixture. 

The only way to keep water out of an asphalt surface is to 
have the voids in the surface mixture as small as possible in size, 
but not necessarily so in volume, to fill them with bitumen of a 
consistency which will permit of contraction and to stiffen the 
latter with a proper amount of filler which will alone permit of 
the use of a sufficiently soft cement. If the interstitial spaces 
are. few in number but large in size, the asphalt occupying them 
will be in such large masses, if the voids are entirely filled, that 



SURFACE MIXTURES. 373 

they will easily yield to stress and cause the surface to mark and 
push and the pavement to appear soft. If the voids are not filled 
water quickly enters and destroys the pavement. If fine sand 
is introduced in proper proportions the size of the interstitial 
spaces is much reduced, the volume of the masses of asphalt filling 
them is reduced in the same way, and the voids can be thoroughly 
filled without danger of movement. This is made more certain 
by the introduction of a filler into the cement, thus stiffening it as 
it exists between the voids. The function of a filler can be seen 
by rolling out two cylinders of a cement of the same consistency, 
one containing 25 per cent of filler and the other none. Their 
ductility or elongation under stress is then found to be as follows: 

AT 78° F. 

Without filler— elongation 20 . 6% 

With 25 per cent filler — elongation 34 . 5 

The part played by the filler in an asphalt surface mixture 
is thus made apparent. 

Fine sand of 100- and 80-mesh size is desirable, since it is evi- 
dent that grains of this size if introduced in the proper propor- 
tions among coarser sand grains must reduce the size of the inter- 
stitial spaces between the grains even if they do not reduce the 
volume of the latter. In this way they play an important part 
in the stability of the pavement, but they play a still more important 
part in making it possible to use a desirable amount of filler in 
the mixture. In the early days of the industry, as it was carried 
on in the city of Washington, it was possible to use only a very 
small amount of filler in the surface mixture and this never 
exceeded 3 or 4 per cent. If a larger amount was added, either 
there or elsewhere, where coarse sands were employed, it was 
found that when an attempt was made to lay the mixture upon 
the street it would not rake or spread with ease and was in a con- 
dition which was known as "bally." It was impossible, there- 
fore, under such conditions to attempt to close up the surface 
of the finished pavement by the use of large percentages of filler, 
although attempts were made to do so. When it was found that 
the most desirable surfaces contained a considerable percentage 
of filler not intentionally introduced into them, and that this- 



374 THE MODERN ASPHALT PAVEMENT 

was accompanied by a similar amount of 100- and 80-mesh 
sand grains, attempts to duplicate these mixtures with the fine 
sand present showed that in the presence of the latter much higher 
percentages of filler could be added without resulting in a " bally " 
condition of the hot mixture on the street. A consideration of this 
state of affairs will quickly show that this is due to the fact that 
in the coarse sand where the size of the spaces between the indi- 
vidual grains were large there was an opportunity for the filler to 
become balled up with the comparatively large masses of asphalt 
cement present there, but when the fine sand was introduced this 
material as it was tossed around in the mixer in a hot condition it 
broke up these balls and made a smooth and homogeneous mix- 
ture which could be raked out on the street with ease. The value 
of sand of 100- and 80-mesh sizes is, therefore, to be attributed 
to the two causes mentioned above: one, its reduction of the size 
of the spaces between the individual sand grains, and, secondly, 
to the fact that it permits the use of a proper amount of filler 
in the mixture by preventing the collection of the filler into bally 
masses. 

SUMMARY. 

The preceding chapter consists of an elaborate discussion of 
the theory of asphalt-surface mixtures which does not admit of 
summarization beyond the statement that the construction of a 
standard mixture is dependent upon an intimate knowledge of 
the behavior of sand and the complete mineral aggregate towards 
the bitumen and of the finished surface mixture towards its 
environment. 

It shows that an asphalt surface to be successful must be so 
constructed as to resist weathering and impact, which are the two 
most serious enemies of such a surface, and it also shows how 
this can be done. 

As the surface mixture is one of the most important elements 
of the pavement the data collected here will be of great interest 
to the asphalt expert or the person desiring to make himself one, 
and also to a very considerable extent to the general reader in 
revealing the amount of skill which is necessary in handling the 
material which enters into the composition of an asphalt surface. 



CHAPTER XVII. 
ASPHALTIC OR BITUMINOUS CONCRETE. 

The term asphaltic or bituminous concrete has been in us* 
for many years to denote a concrete in which asphalt or some other 
bituminous substance has been used as a cementing material 
for a mineral aggregate instead of hydraulic cement. Such a 
concrete has been employed particularly as a foundation for 
heavy machinery, the vibration of which it has been desired to 
do away with where this is a nuisance. Owing to its elasticity 
and lack of rigidity, it absorbs and does not transmit shock. 1 

As a pavement or roadway bituminous concrete in which coal 
tar was the cementing material was exploited to a very large extent 
nearly half a century ago in the United States. Roadways of 
this description were laid in Washington, D. C. in the early 70's, 
among them one on Connecticut Avenue by C. E. Evans in 1873, 
under a contract dated August 7, 1872. This pavement was a 
failure owing to the character of the cementing material and was 
resurfaced and covered up with a new one after a short time. It 
remained in place, however, as a foundation of the roadway, 
until 1906, when it was removed, on repaving the street, and the 
construction of a hydraulic concrete foundation. The author 
was present when the old surface was torn up, and collected 
specimens of the original Evans concrete as being of interest and 

1 See Delano, "Twenty Years' Practical Experience of Natural Asphalt 
and Natural Bitumen," London, E. & F. N. Spon, 1893. Malo, "LA.S- 
phalte. Son Origine, Sa Preparation, Ses Applications/' Paris, 1866 and 
1898. Letouze et Loyeau, "Traite pratique des Travaux en Asphalte/-' 
E. Bernhard et Cie, Paris, 1897. 

375 



376 



THE MODERN ASfHALT PAVEMENT. 




ASPHALTIC OR BITUMINOUS CONCRETE. 



377 



as illustrating the earliest bituminous concrete in use as a road- 
way, which has been preserved. A sawn section of this pavement 



■ ' ■ i»"hSl Mil 
IB - - fig " :'Mf,. »». M ! m9 


' i[H HB 


Jk ■■■* ^ - •- •*" i",--f *• '^^ 


J1& 


s 4 * - 


■ . 


• ^1 






1 ' <*:> t &- V 




"" " 


i ■• 'J- % - - s& » : 




■^■mbm 




J 



B 
O 

fcjO 
O 

02 



ft 



is shown in Fig. 10. It will be seen that the mineral aggre- 
gate in this bituminous concrete consists of broken stone of 
various sizes, sand and coal tar as a cementing material. This- 



378 



THE MODERN ASPHALT PAVEMENT. 



is more strikingly shown by an analysis of the material which 
resulted as follows. 



EVANS' CONCRETE PAVEMENT, 1873. 



Entire 
Pavement. 



Bituminous matter soluble in CS 2 3 . 0% 



Mineral matter pass 



ng 200-mesh screen 3.2 



10 



I inch 

i ( ( 

2 



37.1 

2.7 
10.5 
14.3 
14.7 
14.5 

100.0 



37.1 
13.2 

43.5 



Mineral 
Aggregate. 



3.4% 3.4 
33.2 38.2 

2.8 
10.8 
14.7 



13.6 



15.2 
14.9 

100.0 



44.8 



Density of concrete 2 .73 

" stone 2.86 

" sand 2.65 

Voids in mineral aggregate 23 . 7% 



The concrete does not differ in a great degree from similar 
material which has been used as street roadways within the last 
few years, at least as far as the grading of the mineral aggregate 
is concerned, as will appear from analyses which follow. Much 
of it was laid in Washington at the time mentioned, but all of 
it was unsatisfactory and required resurfacing within a few years. 
It is of interest only as showing that a bituminous concrete was 
recognized as long ago as 1873 as a possible material for paving 
purposes. 

Asphaltic concrete, as far as the author is informed, was first 
proposed for use as a pavement in 1896. A sidewalk of this 
material was constructed on West Avenue at Sixth Street, in 
Long Island City, N. Y., at the plant of the Barber Asphalt 
Paving Company at that point. The development of the concrete 
used was the result of some investigations conducted to determine 
whether a satisfactory material of this description could be assem- 
bled from a well graded mineral aggregate and an asphaltic cement 
which would be suitable for lining a canal. In order to obtain 



ASPHALTIC OR BITUMINOUS CONCRETE. 
COAL-TAR CONCRETES, 1902-1906. 



379 



Cleveland, 
Ohio. 



1902 



St. Louis, 
Mo. 

1903 



St. Louis, 
Mo. 



1904 



Toronto, 
Ont. 



1904 



Water- 
bury, 
Conn. 

1905 



Soluble in CS, 



Pass 



ng 200 screen 

100 " 

^-inch screen 



3.9% 

7.1 
18.8 
13.9 



3.4% 
2.9 
12.0 
4.2 
6.6 



5.0% 

5.6 
23.8 

8.2 
19.0 



56.3 



Retained 1 
Total . . 



55.6 
15.3 



38.4 
.0 



5.5% 

5.0 
26.0 
14.7 
17.5 
16.8 

8.4 

6.1 



4.3% 

5.5 
21.9 

6.3 

3.6 
10.8 
23.3 
24.3 



100.0 



100.0 



100.0 



100.0 



100.0 





Spring- 
field, 
Mass. 

1905 


Cam- 
bridge, 
Mass. 

1905 


Boston, 
Mass. 

1905 


Lynn, 

Mass. 

1905 


Port 

Huron, 

Mich. 

1906 


Soluble in CS 2 


5.3% 

3.3 
29.4 
11.4 

3.3 
12.8 
12.5 
22.0 


5.3% 

4.4 
30.9 
15.9 
21.4 
15.6 

6.5 
.0 


4.8% 

4.7 
26.5 
14.4 
24.0 
23.0 

2.6 
.0 


6.2%* 

5.5 
19.0 
10.5 
23.1 
23.1 
10.1 

2.5 


6.9% 

1.8 
13.7 
13.2 
10.9 

5.5 

4.6 
43.4 


Passing 200 screen 

" 100 " 

' ' ^-inch screen . . . 

i " " ... 

t< 3 H << 

4 • • • 

1 " " ... 

Retained 1 " " ... 


Total 


100.0 


100.0 


100.0 


100.0 


100.0 







* Percentages of components used. 



a mineral aggregate with a small percentage of voids, it was 
recognized that it would be necessary to combine the coarsest 
stone which was to be used with finer stone to fill the voids in 
the coarser, and this again with sand and fine mineral matter to 
further reduce them. The relative proportions were determined 
by experiments. 

In the actual production of this concrete mixture, crushed 
stone, the largest particles of which would pass a screen with 
openings three-quarters of an inch in diameter, but containing 
a considerable amount of quarter inch material, was heated and 
separated into two sizes, coarse particles and those passing a 



380 THE MODERN ASPHALT PAVEMENT. 

screen with openings three-eighths inch in size. Sand, such as 
was ordinarily used in the paving business, was heated separately. 
Finely ground limestone was used cold. These four components 
were then mixed while the first three were hot, and to them was 
added an asphalt cement of proper consistency in the predeter- 
mined proportions. The resulting concrete mixture was tamprd 
into a wooden form from which the resulting block was removed 
on cooling. Its dimensions were 3X4X1 in feet. It was a very 
successful piece of bituminous concrete, and after exposure to the 
sun and weather for nine years had preserved its form and showed 
no signs of deterioration. It was very carefully analyzed in 
1905, with the following results : 

Test number .- 81662 

Bitumen 7.9% 

Passing 200-mesh screen 9.3 9 .3 

10 " " 34.7 

8 " " 6 

|-inch screen 6.1 6.7 

* " " 31.6 

1 " " 9.8 

Retained 1 " " 41.4 



100.0 
Voids in mineral aggregate 15 .0% 

This concrete, as appears from the abcnra data, consists of 
a well graded mineral aggregate, the voids in which amount to 
only 15% of its volume, cemented together into a resistant mass 
by an asphalt cement. It was so satisfactory that its application 
as a surface for pavements at once suggested itself. In order to 
determine whether it could be used in this way practically, a 
driveway in a store-house at the plant of the Barber Asphalt 
Paving Company Long Island City, covering an area of 36 square 
yards, was laid with such a concrete, the character of which is 
shown by the following determinations made upon a sample of 
the surface in 1905, after the roadway had been subjected to the 
traffic of loaded vans for nine years, with no repairs. 



ASPHALTIC OR BITUMINOUS CONCRETE 381 

Test number 80951 

Bitumen 6.2% 

Passing 200-mesh screen 5.1 5.1 

10 " " 33.6 

8 " " 3.1 

" i-inch screen 9.3 12 .4 

" $. " " 27.0 

1 " " 15.7 

Retained 1 " " 42.7 

100.0 

Voids in mineral aggregate 14 . 1% 

The general similarity between the concrete of the driveway 
and the block is evident. The latter contains more coarse stone, 
but the voids in the mineral aggregate are practically the same, 
14.1 as compared to 15.0 per cent in the samples examined. The 
fact that an asphaltic concrete, the basis of which is a mineral 
aggregate of such compact and dense nature as to contain a very 
low percentage of voids, could be turned out, in a rational and 
not an empiric way, on different occasions, and successfully 
placed in forms and as a roadway was thus demonstrated. 

At that time there was no sidewalk in front of the office and 
laboratory of the Barber Asphalt Paving Company on West 
Avenue, the building having been only recently completed. In 
view of the success met in laying the driveway, it was decided 
to construct this walk of the same material, so that its behavior 

Test number 82157 

Bitumen 7.3% 

Passing 200-mesh screen". 8.2 8.2 

" 10 " " 24.2 

" 8 " " 1.2 

" \ -inch screen 7.9 9.1 

\ " " 33. 

1 " " .............. 20.3 

Retained 1 " et .0 51.2 

100.0 

Voids in mineral aggregate ............ 15. 5% 



382 THE MODERN ASPHALT PAVEMENT. 

might be observed in the open air. The area covered was about 
90 square yards, and the surface was supported upon a broken 
stone and cinder foundation. The character of the mixture 
laid is shown on the bottom of preceding page, as determined in 
1905 from several samples taken from the pavement at that time. 
In producing the preceding mixture, the records show that 
the components were combined in the following proportions: 

Stone, passing £-inch screen 450 lbs. = 45 .2% 

" f " " 125 " = 1.2.8 

Sand, " 10 mesh screen 2.",0 " = 25.6 

Filler, dust, 60% passing 200-mesh- 

screen 50 " = 5.1 

Asphalt cement 100 ' ' = 10 . 3 

975 100.0 

The mineral aggregate, it will be seen, as has already been 
mentioned, was made up of two sizes of stone, of sand, and a 
filler in the shape of a fine mineral dust. They were combined 
in such proportions as to make a very dense aggregate having 
voids, varying on account of some segregation in laying the mate- 
rial, of from 13 to 17 per cent, and averaging 15.5 per cent. This 
aggregate was assembled on the previously well established prin- 
ciple that to accomplish the desired result — a dense concrete — 
the voids in the coarsest stone must be filled with particles of 
suitably smaller size, and the voids in this combination again 
with other still smaller ones — in this case sand — and still further 
with material finer than sand — in this case mineral dust. The 
actual proportiors were worked out by packing the materials 
solidly in a box holding a cubic foot and determining the percent- 
ages of each necessary to obtain the densest aggregate. 

The bituminous concrete made in this way has given great 
satisfaction for eleven years. When a demand arose for such a 
mixture for roadways, as a novelty, it was very evident that it 
was only necessary to duplicate the Long Island City mixture 
of 1896. This was done on a considerable scale in Muskegon, 
Mich., in 1902, on Muskegon Avenue, under the author's direction. 
The area covered was 10,736.16 square yards. The mixture had 



ASPHALTIC OR BITUMINOUS CONCRETE. 383 

the following composition, as shown by a very careful analysis 
made of a specimen taken from the street in 1905: 

Test number 81117 

Bitumen 7 .4% 

Passing 200 mesh screen 7.4 7.4 

" 10 " " 34.0 

8 " " 2.8 

" ' {-inch " 11.2 14.0 

h " " 18.0 

1 " " 19.2 

Retained 1 " " 37.2 

100.0 

Voids in mineral aggregate 16 .8% 

A comparison of these data with those for the mixture of 
1896 shows the striking resemblance of the two materials, al- 
though the Muskegon mixture contained less stone. The pave- 
ment was, in fact, a duplication of the Long Island City work. It 
has proved entirely satisfactory after six years use. 

In the following year, 1903, an asphaltic concrete pavement 
was laid in Owosso, Mich., with a mixture having a similar com- 
position, but containing more coarse stone. 

Test number 80904 

Bitumen 7.4% 

Passing 200 mesh-screen 5.2 5.2 



10 " " 

" 8 " " 


29.4 

2.2 


J-inch screen 


3.5 

9.8 


Ct 1 C C ( c 

Retained 1 " ' ' 


33.5 

9.0 







5.7 



52. 



100.0 
Voids in mineral aggregate 13 . 2% 



Similar surfaces have been laid in Scranton, Pa., Paterson, 
N. J., Newark, N. J., in the Borough of Richmond, New York City, 



384 



THE MODERN ASPHALT PAVEMENT. 



and elsewhere in subsequent years. They have proved satis- 
factory on streets of light traffic where street car tracks are absent, 




Fig. 12. — Asphaltic Concrete Sidewalk, Long Island City, New York, 1896. 

but, like all pavements, cannot be maintained against rails that 
are not rigid. They will not withstand heavy traffic, as the 




Fig. 13. — Asphaltic Concrete Surface, Broadway, Paterson, N. J., 1906. 

coarse particles of stone ravel out under the continuous impact 
of the horses' hoof and shoe, the commonest cause of deterioration 
of all forms of street pavement. If, however, the asphaltic con- 



ASPHALTIC OR BITUMINOUS CONCRETE. 



385 



crete is covered with an inch of standard surface mixture the 
resulting pavement has been found to exceed for durability any- 
thing that has been hitherto constructed, especially where there 




is a possiblity of vibration, as along street railway tracks and on 
a base which is not perfectly rigid. There is every evidence 
that this form of construction will be the one to be adopted on 



386 



THE MODERN ASPHALT PAVEMENT. 



streets of heavy traffic in the future, and its use is recommended 
by the author where trying conditions are to be met. This form 
of construction is shown in secnon in Fig. 16. 




pq 






Production of Asphaltic Concrete. — Asphaltic concrete can be 
turned out in any plant which is fitted for the production of the 



ASPHALTIC OR BITUMINOUS CONCRETE. 



387 



binder and surface mixture for the ordinary form of sheet asphalt 
pavement, with certain modifications, permitting of the separation 
of the stone into two sizes after it has been heated in the ordinary 
heaters provided for binder stone and storage in separate bins. 
For this purpose the heated stone is passed over a revolving 




Fig 16. 



apparatus provided for this purpose. The three materials are 
then weighed or measured out in the predetermined proportions, 
screen of sheet metal having perforations f inch in diameter. The 
finer stone which passes the screen is collected in one bin and 
the coarser into another. There is no necessity for separating them 
into a greater number of sizes. The sand is heated in the ordinary 



388 THE MODERN ASPHALT PAVEMENT. 

the dust or filler added, and the combined aggregate thoroughly 
mixed in the usual pug mill, after which the asphalt cement is 
added and the mixing continued until the concrete is homo- 
geneous. Portions of the mixture are then compacted under a hot 
tamper upon a firm surface to determine how satisfactory it is. 
The hot tamper should bring to the surface of the specimen a 
slight excess of bitumen, if this is present in correct amount. 
If the surface remains dry, more asphalt cement must be added, 
but if it is too greasy, it must be reduced. On cooling tha specimen 
may be broken. 

If the concrete is to be used as a binder course, there must be 
no excess of bitumen and a slight deficiency of sand over that 
required to fill the voids in the stone, as otherwise the surface 
will be too readily displaced on such a course under traffic. 

The character of the concrete, in either case, can be determined 
also by its appearance in the truck after the haul from the plant 
to the street. Where it is to be used as the surface to carry 
traffic, it should have settled to a compact mass, the top of which 
should show a slight excess of bitumen as a rich coating, whereas 
if it is intended for a binder course no excess of bitumen should 
appear and there should be some evidence of the coarser particles 
of stone at the top of the load. 

In either case, the asphalt cement should be much softer than 
that in use in the ordinary surface mixture containing sand alone. 
The penetration should be about 90, as determined by the Bowen 
penetration machine, 

SUMMARY. 

An asphaltic concrete pavement is not a novelty. Such pave- 
ments have been laid for over twelve years, and have proved 
satisfactory where not exposed to heavy traffic. On streets like 
Broadway, in New York, it is unsatisfactory. 



CHAPTER XVIII. 
ASPHALT BLOCKS. 

Pavements composed of blocks of asphaltic concrete in which 
the coarsest particles of the aggregate are no larger than J or J 
inch in size, have been laid for a great many years with considerable 
success on streets of light or very moderate traffic. The idea 
of making such blocks originated in a crude way in San Francisco 
in 1869. The first Board of Commissioners of the District of 
Columbia stated in its report of 1878 that an experimental piece 
of pavement of this description had been laid in Washington on 
E Street, the Board having been influenced to do so by favorable 
reports of its durability in Providence and Philadelphia. It was 
not, however, until the application of powerful mechanical presses 
to the compression of the blocks in 1880 that they proved at all 
successful. 60,774 square yards of this form of pavement had 
been laid in Baltimore up to June 30, 1885, and 45,000 had been 
laid in Washington on a foundation of five inches of bank gravel 
and a cushion of two inches of sand. The Engineer Commissioner 
of the latter city reported that the character of the block had much 
improved in the two preceding years. The blocks were four inches 
deep, five inches wide and twelve inches long. Many of these 
pavements are in existence to-day in satisfactory condition, having 
been subjected only to the most moderate travel on residence 
streets, and prove the adaptability of such surfaces to similar 
conditions. The blocks were of sufficient depth to support each 
other laterally. By June 30, 1889, the area of block pavements 
in Washington had increased to 117,164 yards, and it had spread 

389 



390 THE MODERN ASPHALT PAVEMENT. 

to other towns, notably, Baltimore, Md., and Chester, Pa., where 
40,000 square yards of block had been laid. This form of pavement 
made no great further progress until 1896, when the amount reached 
200,000 yards, 33,874 of this being in the Borough of Man- 
hattan, and the blocks being 4x4x12 inches in dimension. In 
1901 the block as at present laid, 3X5X12, was brought out 
and laid on East 27th Street from Third to Madison Avenues, 
since which time large areas of blocks of this description have 
been put down with varying success, the pavement failing uni- 
versally under heavy travel and requiring renewal or extensive 
repairs in from one to two years, and revealing the fact that an 
asphalt block pavement at least, as at present constructed, is 
suitable only for residence streets of the lightest travel. The 
causes of this are not far to seek after a study of the nature of 
the blocks and of the technology of the industry. 

Asphalt blocks consist of a mineral aggregate and a bituminous 
cementing material, as is the case in the sheet or monolithic 
asphalt pavement. They differ essentially from the latter form 
of construction in that the aggregate is much coarser, containing 
particles as large as \ or | inch in size, while the cementing mate- 
rial is of a much harder consistency, to enable the blocks to be 
handled in the course of their transfer from the place where they 
are made to the street and to be stored for some time without 
losing their shape. Blocks of the ordinary surface mixture which 
is used in the construction of a sheet asphalt pavement which 
would withstand the heaviest travel could not be transferred from 
the plant to the street without doing so, and under a hot summer 
sun would soon become a monolithic mass in the street, even if 
it were possible to place them there before they were so much 
out of shape as to make it impossible to lay them. One of the in- 
herent defects in asphalt blocks, at least as they have been laid 
up to the present time, is that the cementing material which binds 
them together is too hard to enable the block to resist heavy travel, 
and they have gone to pieces, especially in cold and wet weather, 
after being exposed to it for but short periods of time. In ad- 
dition, the aggregate of an asphalt block is not a satisfactory one 
as far as grading is concerned. It consists to-day of crushed 



ASPHALT BLOCKS. 



391 



trap-rock or similar hard stone, which will pass a screen having 
openings f inch in diameter. Whether these screenings are made 
particularly for the purpose with steel rolls or are the finer 
portions of stone which has been crushed for concrete, they al- 
ways contain an excess of particles of a size which will pass a 
screen of ten meshes to the linear inch, and be retained on one of 
twenty meshes. The screening of such material does not vary 
largely from year to year, as can be seen from the following figures: 



Year. 


1906 


1907 


Passing 200-mesh screen 


11 


18 


13 


18 


15 


20 


" 100 " " 


8 


13 


6 


8 


7 


10 


80 " " 


3 


5 


2 


3 


3 


4 


50 " " 


8 


13 


8 


11 


8 


11 


" 40 " " 


4 


6 


3 


4 


3 


4 


30 " " 


6 


9 


7 


10 


7 


10 


" 20 " " 


6 


9 


9 


13 


9 


12 


" 10 " " 


17 


27 


24 


33 


21 


29 


' ' L ^-inch mesh screen . 


37 




28 




27 







100 


100 


100 


100 


100 


100 



In 1906 there was a considerably larger percentage of grit 
than in 1907, but otherwise the grading did not differ essentially. 
If asphalt blocks are, however, regarded as being composed of 
small particles of stone or grit, the voids in which are filled with 
a standard mixture such as had been found most desirable for 
sheet asphalt surfaces, the portion of the crushed trap-rock which 
plays the role of sand, it will be seen on calculation, has a grading 
which is entirely "unsuited for the purpose for which it is used, 
and one which would never be employed in the sheet asphalt 
industry. There is no way of modifying this grading except 
by rejecting the excess of 10-mesh material, and even then there 
remains a deficiency in the grains passing sieves of 80- and 100- 
meshes, while the expense involved makes it quite impossible 
to attempt such a modification. The crushed rock must be used 
just as it comes from the rolls or from the crusher, and the grading 
is uniformly bad, as can be seen from the analyses of blocks made 



392 THE MODERN ASPHALT PAVEMENT. 

by various firms and corporations. There would be no possi- 
bility of obtaining good service from a sheet asphalt surface with 
a mineral aggregate of such grading, and it is not surprising, 
therefore, that asphalt blocks do not wear when subjected to 
heavy travel, especially as most blocks are made, as has been 
said, with an asphalt cement, which is far too hard and which, if 
used in a sheet asphalt pavement, would result in scaling of the 
surface during damp, cold weather. 

The question at once arises as to what opportunities are possible 
for modifying and improving the character of an asphalt block. 
As a modification' of the grading of the crushed trap-rock is im- 
practicable for economic reasons, if a more satisfactory mineral 
aggregate is to be obtained, recourse must be had to materials 
found in nature which can be combined to give the desired grad- 
ing, such as a well graded sand or clean trap-rock grit of proper 
size or gravel. There would be no difficulty in obtaining proper 
sands, such as are used in the sheet asphalt industry, but suitable 
gravel would be more difficult to find. An opportunity, however, 
is afforded for improving somewhat the character of the block 
in another direction, by the use of a more suitable asphalt cement 
than that which has been in use hitherto, one which is not so 
susceptible to extremes of temperature. With such a material, 
a consistency which would be suitable for making a block which 
would not be so brittle at low temperatures could be used, and, 
at the same time, the block would not be so soft under a summer 
sun as to lose its shape on storage without lateral support or 
under pressure before being placed in the street. Such a cement 
is found in one prepared from Gilsonite and an asphaltic flux. It 
can be used of a much softer consistency than one made with 
Trinidad or Bermudez asphalt without danger of producing a 
block which will not retain its shape. This can be seen by a com- 
parison of the consistency of the three cements, as they are used in 
making blocks, at different temperatures. 

Penetration-millimeters. 
32° F. 77° F. 1 10° F. 

Trinidad asphalt 2 1.4 6.8 

Bermudez asphalt 2 1.3 7.3 

Gilsonite 5 2.6 7.5 



ASPHALT BLOCKS. 



393 



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394 THE MODERN ASPHALT PAVEMENT. 

Under any circumstances, asphalt blocks which are suitable 
to resist heavy traffic will be sufficiently soft to become, in summer, 
almost a monolothic surface under travel. 

The character of asphalt blocks is usually determined both 
by chemical and physical tests, the latter being the more important 
and including determinations of density, modulus of rupture, 
and loss from attrition in a rattler of the type used in testing 
paving brick. The results of such tests on various blocks produced 
by the most prominent manufacturers are presented in the ac- 
companying table. 

SUMMARY. 

Asphalt blocks are very satisfactory under certain circum- 
stances as a form of pavement for residence or light traffic streets, 
but experience has shown that such a pavement is unable to 
wear for any length of time under heavy traffic. 



CHAPTER XIX. 

THE PROCESS OF COMBINING THE CONSTITUENTS INTO A 
SURFACE MIXTURE. 

Asphalt cement of a desirable nature, a sand or sands which 
will afford a satisfactory grading, and a sufficiently finely divided 
mineral matter for a filler being available, it is necessary that 
these materials should be combined with great care, skill, and 
uniformity in order to produce a surface mixture which shall be 
free from criticism. 

To bring about this combination some type of plant is necessary 
which shall make it possible to meet the following conditions; 

1. To feed a sand or mixture of sands into the sand heater 
with great regularity and to have it pass through the drum in 
such a way that it is uniformly heated and the particles not segre- 
gated according to size. 

2. To raise the heated sand to a temperature of from 330° 
to 380° F. as it emerges from the heater, without reducing its tem- 
perature essentially, pass it through a sieve which shall remove 
all particles larger than those passing a laboratory screen of 
10 meshes to the inch, and collect it in some form of bin where 
it can be held for some time without too much radiation and 
from which it can be drawn without delivering at one time a finer 
and at another time a coarser material. 

3. To have a melting-tank where asphalt cement can be main- 
tained in a melted condition and at a uniform temperature and 
provided with suitable means of agitation, either air or steam. 

4. To have suitable provisions for determining accurately the 
weight or volume of the constituents entering into the compo- 
sition of the surface mixture. 

395 



396 THE MODERN ASPHALT PAVEMENT. 

5. To have a mixer which shall make an entirely uniform and 
homogeneous combination of all the constituents which go into it. 

6. With a satisfactory plant it is equally necessary to have 
a foreman to run it who not only understands how to make every- 
thing move uniformly but who has had experience in and under- 
stands the technology of the industry and the reasons for each 
step that is taken. 

These necessities may now be considered in greater detail. 

Sand. — To obtain a sand of satisfactory grading it has already 
been shown that it is usually necessary to mix two or more sands. 
To obtain a uniform mixture from sands which will give a proper 
grading requires care and attention and proper facilities for storing 
the sand conveniently in the rear of the sand-drums. The two 
or more sands are then wheeled up or shovelled in separate piles 
in the neighborhood of the bucket elevators, which are to elevate 
it to the drums. The sands are then fed into the buckets with a 
shovel or hoe by laborers in such proportions as may be found 
by experiment to be necessary. This feeding must be carefully 
watched, as, owing to the class of labor employed, little depend- 
ence can be placed upon the laborer himself. If the feeding is 
irregular the surface mixture will also be irregular. The regu- 
larity of the feeding is determined on the platform by sifting. 

To obtain uniformity in the temperature of the sand the type 
of sand-heater must be a satisfactory one and the firing must 
be as carefully done as with a steam-boiler. Only experienced 
firemen should be employed and they should be instructed to 
watch the temperature of the effluent sand closely. 

The hot sand falls from the drums into a boot, from which it 
is raised to the sand -screen over the sand-bin. This elevator 
should be well closed in to prevent radiation and the screen and 
bin should also be enclosed. 

The screen should be cylindrical or conical in shape; in the 
latter case, 3 feet in diameter at one end and 20 inches at the 
other. It should revolve about 12 revolutions per minute. At 
the end of the larger diameter it is covered for half of its length 
mth. cloth of 10 meshes to the inch, No. 22 wire. The remainder 
should be 8 meshes of No. 18 wire, the entire length being 5 to 6 feet. 



THE PROCESS OF COMBINATION. 39? 

Angle-irons placed lengthwise of the screen at each quadrant 
will strengthen it and increase its capacity by throwing the sand 
about. 

The sand should not be allowed to fall into the bin irregu- 
larly and from whatever point it passes the screen. It should 
all fall into a hopper which opens over the centre of the bin. This 
is quite necessary to prevent segregation, as otherwise the fine 
sand would pass the screen first and go to one side of the bin, 
the coarser particles collecting at the other. 

At best a certain segregation results on drawing sand from 
the bin. Unless the bin is kept more than half full there is a 
tendency to form a hollow cone in the centre of the mass of sand, 
down the sides of which the coarse particles run and accumulate, 
so that every now and then there is a delivery of coarse and again 
a delivery of fine sand. This can only be avoided by not draw- 
ing the bin down too low. 

Various shapes of bin have been suggested, but a cylinder 
and cone or a half cylinder and half cone are probably the best. 
The gate should be in the bottom of the cone and not in the side. 

Segregation is, however, apt to take place in any form of bin, 
and that form which prevents this to the greatest extent is the 
most desirable. 

The temperature at which it is necessary to maintain the sand 
in order to produce a satisfactory mixture will depend on the 
character of the mixture that is being turned out, the nature 
of the asphalt in use, the weather, and the distance to the street 
from the plant. If the mixture is a fine one, carrying much filler 
and bitumen, if Trinidad asphalt is the cementing material, and 
if the weather is cool, 385° F. is not too high a temperature for 
the sand in the bin. If a smaller amount of filler is employed 
the temperature need not exceed 335°. In any case the mixture 
should reach the street at such a temperature that it can be raked 
freely. In the best New York mixtures the temperatures aver- 
age 330° F. The average mixture of the country will reach the 
street at 310°. The above applies to a standard Trinidad mix- 
ture. If other asphalts are used the temperatures must be con- 
siderably reduced, as they will suffer from such heat. The harden- 



398 THE MODERN ASPHALT PAVEMENT. 

ing effect of hot sand on asphalt cement has already been noted, 
and should always be allowed for in those mixtures made with 
susceptible bitumens such as Bermudez and the hard residues 
from petroleums or where the flux in use is one carrying much 
volatile oil. 

Melting-tanks. — The melting-tanks in which the asphalt cement 
is made at the smaller plants or into which it is drawn from the 
refining-tanks at the larger ones should be so constructed that 
no portion of their contents shall become readily overheated. 
The bottoms should be protected from direct flame by a fire- 
brick arch. Agitation is necessary, not only with such an asphalt 
as Trinidad, for the purpose of keeping the mineral matter in sus- 
pension, but with others as well, to keep the material from too 
long contact with the sides of the tank, and of even temperature, 
since convection in melted asphalt results in but a very slow 
motion of the mass. 

Agitation with steam is undoubtedly the best method, as the 
action of air on all oils at a high temperature is very strong, the 
result of blowing an asphaltic residuum at a temperature of 350° 
with air for twenty-four hours being to convert it into a semi- 
solid buttery mass. 

Agitation is also a matter of economy as far as the life of the 
tanks themselves are concerned, as they will burn out very rapidly 
if sediment or coke is allowed to collect in them. 

In plants where a large amount of work is done some pro- 
vision in the form of a pneumatic lift should be made for raising 
the cement to the asphalt bucket, where it is gauged or weighed 
without the aid of manual labor. 

The requisite amount of asphalt should be weighed and not 
measured and the same may be said of the sand. The same volume 
of sand may vary very much in weight according to the way it 
runs into the receptacle. 

The type of mixer in use in combining the constituents is, 
of course, of importance and still more so the way in which it is 
kept in repair and good order. It is usually constructed to mix 
a volume of 9 cubic feet at one operation, but as large a volume as 
18 can be thoroughly mixed in a properly constructed mill and 



THE PROCESS OF COMBINATION. 399 

corresponding economy attained. The mixer should be pro- 
vided with a liner which can be renewed when worn. It should 
be provided with a set of teeth made of chilled iron or having 
steel tips which reach within a quarter of an inch of the lining. 
The teeth should be set on a shaft the bearings of which can be 
raised or lowered by the introduction or removal of shims so as 
to bring the teeth nearer or farther away from the liner. It should 
have a gate which is tight and will prevent the leaking of either 
asphalt or sand. In the larger types of mixer the gate is controlled 
by some power appliance. 

The mixer rests on what is technically known as the platform, 
which is sufficiently elevated to admit a truck beneath. Behind 
the mixer is the sand-box in which the sand and filler are weighed 
or measured out. Over it is the bucket for the asphalt cement 
suspended from a scale. The sand and filler having been weighed 
in the box and the A. C, the technical designation of the asphalt 
cement, in the bucket, the two former are allowed to run out 
through a gate into the covered mixer, which is, of course, in motion, 
or if the sand-box is one that has no gate, it is dumped into the 
mixer. It is allowed to remain there for from 15 to 20 seconds to 
mix the dry materials thoroughly. The asphalt cement is then 
poured or run directly into the middle of the dry mix and not spread 
about over different parts of it, as the mixer teeth will bring all the 
sand to the centre to meet the bitumen, but will not be able to do so 
as readily with the latter. After the introduction of the asphalt 
cement the mixing is continued for about one hundred revolutions. 
The gate to the mixer is then opened and the mixture dropped 
into the truck. 

Where the platform is large enough a testing-room should be 
provided there for the use of the yard foreman; otherwise it 
should be upon the ground in front of the mixer, as in the case of 
a railroad plant. He should have there a set of sand-screens, 
a sand-balance, a flow outfit for controlling the consistency of his 
A. C. and manilla paper for making pat tests of his mixture. He 
should screen samples of sand taken from the boot of the sand- 
drums and from the bin in order to be sure that the sand mixture 
is being fed in the proper proportions and evenly. He should 



400 THE MODERN ASPHALT PAVEMENT. 

make comparative flow tests of the asphalt cement he has in use 
with that of the standard furnished him for the purpose. Finally, 
he should make frequent pats of his mixture to determine whether 
it is carrying a proper amount of A. C. and whether it is properly 
balanced. These points are recognized by the stain made by 
the bitumen on the paper and by the appearance of the surface 
of the hot pat when it is held on a level with the eye. Experi- 
ence is, of course, required to interpret these latter tests and to 
understand the indications which are afforded. In addition 
such samples should be taken on the platform as are needed for 
examination in the laboratory by more accurate methods. 

The Production of Binder. — Binder is turned out in exactly 
the same way as the surface mixture except that the tempera- 
ture and not the grading of the stone is to be watched and the 
mixing is done in a mixer having fewer and shorter teeth. The 
temperature of the binder can be appreciably lower than that 
of the surface. It should certainly not be so hot as to cause the 
asphalt to run off the stone, as in that case it will reach the street 
without sufficient cementing material to hold it together, a result 
often noticed in careless work. 

Types of Plants and Machinery. — In the preceding pages no 
mention has been made of any particular type of plant or machinery, 
as this seemed unnecessary. It is the results obtained and the 
way in which they are attained which are of the greatest interest 
to the engineer and to the private individual to whom this book 
is addressed. One type may do slightly more economical work 
than another or slightly better. If the latter is true it can be 
better judged from the character of the material turned out or 
from the celerity with which the work is accomplished. 

It will be of interest here, however, to describe the type of 
the machinery which the author has found most satisfactory. 

Permanent Plants. — In large cities where a very considerable 
amount of work is done every year a permanent plant will, of course, 
be established, consisting of proper storage, for two or more 
grades of sand, in the shape of bins, which can be readily and 
economically filled from the boats, cars, or other means of trans- 
portation which supply the sand. This material should natu- 



THE PROCESS OF COMBINATION. 401 

rally be handled, for economy's sake, as far as possible by power 
and the bins should be so placed in relation to the sand-heaters 
that as little labor as possible will be necessary to feed the sand 
to the heaters. 

Sand-heaters. — The sand used in different localities varies 
from dry bank to dripping-wet river sand, and the heater is required 
to drive off the moisture and heat to a temperature of 330° F. 
or over the maximum amount of sand per unit of time with the 
minimum amount of fuel. As the result of actual trial of many 
different designs the Iroquois Iron Works has adopted a setting 
of two horizontal revolving drums, fired with induced draft, as 
giving the greatest efficiency. By the proportioning of the size 
of the drum, furnace, and induced draft, all the available heating 
power is obtained, and by heavy construction and perfection of 
details the durability of the machine is assured. 

The drum-shells are made of f " steel plate 20 feet long rolled 
to a 40" diameter circle, and are riveted together with two hori- 
zontal butt-strap joints. These shells are carried at both ends 
by heavy cast-iron spiders. Shafts from these spiders extend 
out beyond the shells and form the journals. The bearing at the 
hot sand end takes the thrust, being grooved similar to a propeller 
shaft-bearing. The bearing boxes are fitted with trunnions allow- 
ing swinging in a vertical plane. The trunnions rest on swivel 
brackets, permitting swinging in a horizontal plane; consequently 
there can be no binding in the boxes, they being able to align 
themselves at all times, a necessary qualification for a drum revolv- 
ing in a furnace. Sheet-steel shelves are riveted the entire length 
of the interior, which give additional heating surface and at the 
same time are continually lifting the sand and allowing it to fall 
through the diameter of the drum. The grates are located directly 
under the cold sand end of the drum-shells. 

By means of a fan the combustion gases are drawn along under 
and back through the drums, coming in contact with the sand, 
which, by the shelves on the interior of the drums, is distributed 
through them. By this method the surfaces of the drum are 
heated by direct radiation from the gases of combustion, and the 
gases, being drawn through the drum and coming in intimate 



402 THE MODERN ASPHALT PAVEMENT. 

contact with the particles of sand, not only draw off the released 
moisture and discharge it outside the setting but also assist in 
heating the sand to the required temperature. This induced 
draft is a valuable feature and, as it is easily regulated, increases 
the capacity and ensures obtaining the maximum calorific value 
from the fuel. Such a sand-heater is illustrated in Fig. 17. 

These drying cylinders are mounted in a brick or steel-plate 
setting, as desired. For permanent installation the brick setting 
is preferred. The steel-plate setting is well shown in the illustra- 
tion, Fig. 17, from which it will be seen that the bearing boxes 
supporting the cylinders are mounted on a built-up framework 
at both hot and cold sand ends. This framework consists of a 
base of riveted channels and steel plate, upon which is mounted 
cast-iron brackets for carrying the bearing boxes. The sides are 
made of \" steel plate reinforced with angles. The roof consists of 
two steel plates. The inner, which is J" thick, is curved to con- 
form to the arc of the drums, thus holding the heat against the 
latter. The outer covering of medium gauge sheet steel is carried 
straight across to form a rain-shed. The inner and outer covers 
are riveted to a trussed angle-iron frame which is absolutely self- 
supporting. The sides, ends, and roof are made in sections and 
bolted together, permitting the entire setting to be dismantled 
into small units which are easily handled and packed for ship- 
ment. For the protection of the steel plate it is customary to 
lay up a lining of one thickness of fire-brick at the sides extending 
two-thirds the length of the setting. The exhaust-fan is mounted 
on a timber frame to one side and can discharge into the air or 
be connected with a dust-collector, as may be preferred. 

The drums discharge into a boot, from whence the hot sand 
is elevated by means of steel buckets on a steel pin chain to a 
rotary screen covered with cloth .of the dimensions which have 
been described. 1 The screen discharges into a steel storage-bin 
of from 6 to 9 cubic yards capacity. From the storage-bin it 
flows by gravity to a triangular-shaped weighing-box mounted 
on a beam-scale. Here the required amount of stone dust is 



1 See page 396, 



tn^ri-iH^iH^riHriUfiljritlllM i lll 




o3 
1=1 

1 



404 THE MODERN ASPHALT PAVEMENT. 

added and the charge brought up to accurate weight ready for 
the mixture. 

Melting-tanks. — For melting the asphalt two types of kettle 
are used, fire and steam. The fire melting-tanks are either cylin- 
drical or rectangular, with semicircular bottom, and are set in 
the furnace with a fire-brick arch between the grates and the bot- 
tom of the tank to prevent too rapid heating, which would tend 
to coke the material on the bottom. The fire melting-tanks are 
now more generally used for small portable plants in small units 
of 4 tons capacity. For larger and more permanent plants the 
steam melting-tanks are preferable. 

The steam melting-tanks are rectangular in shape, contain- 
ing horizontal oval-shaped coils of 1J" pipe. Fig. 18. One 
hundred and twenty-five pounds steam pressure is generally 
used, which gives a temperature in the coil of 345° F. Agitation 
is accomplished in both fire and steam melting-tanks by hori- 
zontal pipes laid at the bottom, with small perforations. To 
these pipes are deliverd either steam at boiler pressure or air 
at about 20 pounds pressure. When the asphalt is melted in 
these kettles it is reduced with the required amount of warm 
flux, which is measured in a special measuring-tank and flows 
by gravity to the melting-kettles. The asphalt cement result- 
ing is now ready for the mixer and is delivered to it in one of three 
ways : In small semi-portable plants a bucket carried by a traveller 
mounted on wheels on a track is run out from the mixer over 
the melting-kettles and the cement dipped into the bucket. In 
many permanent plants the melting-kettles are mounted on a 
structure sufficiently high for the asphalt cement to flow by gravity 
directly into the bucket. The third and very largely used 
method is setting a pneumatic lift just below the bottom of the 
kettles. This pneumatic lift consists of a steam- jacketed steel 
cylinder fitted with inlet- and discharge-pipe, air-pipe, and a system 
of valves whereby the cement flows into the lift from the kettles 
by gravity, and by the operation of suitable air- valves, air-pres- 
sure, which need not be over 5 pounds and is generally the same 
as the agitation pressure, is admitted on top of the cement, thereby 
automatically closing the valve in the intake and forcing the 




Fig. 18.— Steam Melting Tank. 



405 



406 THE MODERN ASPHALT PAVEMENT. 

cement up through the discharge-pipe to the weighing-bucket 
at the mixer. 

Mixer. — The mixer consists of a rectangular-shaped steel shell 
with semicircular bottom, containing two horizontal square 
shafts, upon which shafts are bolted blades, or teeth, as they are 
commonly called. Fig. 20. These shafts are made to revolve 
by gearing at a speed of from 60 to 75 revolutions. The teeth 
are made in two different shapes, called right and left hand, and 
are so set upon the shafts that they work the material horizontally 
towards the centre, and at the same time are continually tossing 
it vertically. The result is that an absolutely homogeneous 
mixture of the sand and asphalt cement is obtained within a 
minute and a half, when the mixer-man pulls a lever, opening 
the slide in the bottom, and the finished topping is discharged 
into the wagon ready for hauling to the street. 

Where a plant has but one mixer for turning out both sur- 
face mixture and binder it is provided with another shaft for 
carrying shorter teeth at much wider intervals. This shaft re- 
places the one used for surface mixture when binder is to be pro- 
duced. 

Portable or Semi-portable Plants. — In cities where work is 
only done at intervals and where the amount is not sufficiently 
great to justify the construction of a permanent plant, portable 
or semi-portable plants are used. 

The first type of portable plant consisted of two railroad flat 
cars, one to carry the boiler and melting tanks and the other for the 
sand heaters, with the mixing platform between the cars when 
the plant was set up for use. Such a plant is illustrated in Fig. 
21. The cost of setting up and taking down this form of 
plant when moving from place to place was rather large. The 
plant has therefore been modified to occupy a single car, render- 
ing the cost of putting it in operation extremely small. A plant 
of this type, as manufactured by the Iroquois Iron Works, is 
shown in Fig. 19. 

The semi-portable plant is one which is readily taken down 
and erected, but is not fixed upon a car. It consists of a steel 
tower with mixer platform, as illustrated in Fig. 22, which is 
accompanied by the necessary melting-tanks, usually heated 



THE PROCESS OF COMBINATION. 



407 



by fire. This type of plant has been found very successful in 

late years and has a large future before it for work in small towns. 

Plants of the two previous types require skilled handling and 

close attention, but with a good foreman and engineer equally 




Fig. 19. 

good work can be turned out from them as from a permanent plant, 
and they are highly recommended by the author. 

Bituminous Concrete Plant. — For the production of bitu- 
minous concrete any of the previous types of plant will serve, if 
the screen over which the heated material passes is arranged so 
as to separate the heated mineral matter into three sizes, sand, 
fine stone passing openings f inch in diameter, and coarse stone 
up to f inch in size, and if the bin is divided into compartments 
to hold these separate grades. A special form of plant is not 
required for this purpose, nor is it necessary to separate the stone 
into more than three sizes, as has been shown by the successful 
work done in this way as long ago as 1896. 




o3 

Oh 

o 



o 




Fig. 22. — Semi-portable Mixing Platform. 



410 



THE PROCESS OF COMBINATION. 411 

SUMMARY. 

This chapter describes the process of combining the con- 
stituents into a surface mixture, including the machinery and 
plant necessary for heating the sand and mixing the hot min- 
eral aggregate with asphalt and the type of tanks necessary for 
melting the latter. 



PART V. 

HANDLING OF BINDER AND SURFACE MIXTURE 
ON THE STREET. 



CHAPTER XX. 

THE STREET. 

Transportation of the Materials to the Street. — The transpor- 
tation of the binder and surface mixture from the plant to the 
point where the pavement is being constructed is something that 
cannot be undertaken carelessly and with no other thought than 
merely getting it there. In the case of the binder the only con- 
sideration is that it be so protected that it will not become cold. 
The condition of the surface mixture when it reaches the street 
is much more influenced by the conditions to which it has been 
subjected en route. In the early days of the industry, in Washing- 
ton, D. C, for instance, the old-fashioned dump-cart, holding 
from 18 to 27 cubic feet, was in use. Aside from a matter of 
economy, this is the ideal way to haul the material. Later on, 
as the size of the mixer was increased in the larger cities, trucks 
were employed which would hold six batches of 18 cubic feet, 
or six tons. It was soon found that this method of transporta- 
tion was unsatisfactory, as the larger mass of surface mixture, 
during the long hauls which are unavoidable in cities of the size 
of New York and the constant jarring over rough pavements, 
became so compacted that it was difficult to break it up after 
it was dumped on the street, especially if the mixture was a dense 
one carrying a large percentage of filler and asphalt cement. To 

412 



THE STREET. 413 

offset this disadvantage, however, the larger mass loses heat much 
less rapidly than is the case with the smaller load, and this is a 
distinct gain in cold weather and for repair work. A medium 
course is, therefore, now pursued and loads of about four tons 
are hauled. 

In the smaller cities and towns the question is often a serious 
one, as the trucks available locally are often not suitable for hauling 
surface mixture. The worst type is the ordinary dirt truck which 
dumps by turning over slats which form the bottom of the truck. 
This truck does not protect the mixture from cooling rapidly, and 
in dumping the entire mass is so loosened up as to be still further 
cooled, while much of the material is lost by being carried away 
on the running-gear. 

Whatever the form which the load may take, the surface should 
be protected from the air, at all seasons of the year, by tarpaulins. 
The loss in temperature, if the protection is suitable, will not 
exceed 10° from plant to street in two hours, or often after longer 
intervals, in warm weather. 

It has been found possible to transport large masses of hot 
surface mixture by rail or by scow for long distances. As an example 
of this may be cited work done in New Rochelle, N. Y., in 1899. 
Three hundred tons of mixture were placed on a scow at Long 
Island City, N. Y., and taken by a tug to the point where the sur- 
face was to be laid. Owing to the inclement weather it was impos- 
sible to place the material for thirty hours, but the majority of 
it was in good condition to be laid at that time after the outer 
cooled portions had been removed. The asphalt pavement laid 
in this way has been entirely satisfactory. 

Construction Work on the Street. — Of the work of construction 
of an asphalt pavement on the street consideration need be given 
only to that portion above the base, that of the latter involving 
no principles which have not already been exploited. In earlier 
pages the desirable characteristics of a base have been shown, 
and it is here assumed that the bituminous surface is to be applied 
to such a base. 

The Binder Course. — In general a binder course is the first 
applied. In the description of the preparation of the binder 



414 THE MODERN ASPHALT PAVEMENT. 

it appeared that it was sent to the street at a temperature some- 
what lower than that of the surface mixture. Arriving there it 
should be dumped sufficiently distant from the point where the 
spreading is to be begun or from the point where the previous 
load ended to permit of turning all the material over without 
rinding it necessary to finally distribute any of the binder over 
the base at the point where it has been dumped. This is quite 
necessary, although not as much so as in the case of surface mixture, 
to permit of spreading the binder course evenly, that portion 
lying at the point where the load was dumped being consider- 
ably compressed by the fall and the weight of the incumbent 
mass, so that were this not shovelled over the thickness at this 
point would be greater than elsewhere in the street. 

The surface of the load of binder should be bright and glossy, 
as should the whole mass after it has been dumped. On the 
other hand, there should be no excess of bitumen, as evidenced 
by asphalt running from the bottom of the truck or by too great 
richness of the bottom of the load. Too hot stone may cause 
the bitumen to run off the binder. One should not be misled 
by such an occurrence into the belief that the load is too rich. 
In such a case, however, the surface of the load will generally 
be dead. Unless the stone is covered with a bright coat of 
bitumen the binder will have no coherence and should be re- 
jected. 

The binder is spread with rakes with long tines. It may be 
allowed to cool to a very considerable degree before rolling. If 
rolled too hot it will be much more liable to displacement and 
to being picked up by the roller. It should be rolled directly 
with a steam-roller weighing from five to seven tons. 

Immediately after rolling it is ready for the application of 
the surface. If the surface is not applied at once the binder 
should be protected from becoming soiled by traffic or otherwise. 
A slight coating of dust will do no harm. The hauling of a 
sufficient amount of surface mixture over it to cover it should not 
break it up. If this happens, except on a weak base, it is a sign 
that it is not of the best quality. 

Too often the thickness of binder specified is too small, and 



THE STREET. 415 

in this case it is impossible to lay it so that it will not break up 
to a certain degree in putting on the surface. An inch of binder 
is never satisfactory. Binder is composed of stone the larger 
particles of which are at least an inch in diameter. It is readily 
seen that no satisfactory bond of such materials can be obtained 
in such a thickness. 

Where an asphaltic concrete course is substituted for an open 
binder this must be spread with shovels and the back of the rake. 
The tines should not be used at all, since they have a tendency 
to pull the larger stones to the surface and cause a segregation of 
the material. 

The Surface Course. — The mixture which is to form the sur- 
face should arrive upon the street at a temperature which cannot 
be defined in degrees of the thermometer. It should be hot enough 
to work freely under the rake if it has a properly balanced mineral 
aggregate, but in no case should exceed in temperature one which 
the particular asphalt cement can resist without being too much 
hardened, especially in the mixer when being violently agitated 
with hot sand in contact with air. As different asphalts are very 
variable in respect to their volatility and stability, the extreme 
temperature to which mixtures made with them may be heated 
is quite different. This has already been shown on previous 
pages. The temperature will also vary with the character of 
the mineral aggregate. A dense mixture may be heated much 
hotter without injury than an open one. As a general rule, it 
may be laid down that some dense Trinidad mixtures, such as 
that made with a Portland-cement filler, may with safety be raised 
to a temperature of 340° to 350°, if it is necessary, in cold weather. 
By this it is not meant that such a temperature is desirable if 
the mixture can be worked at a lower one, but that no danger 
will be incurred by its use which is commensurate with the dis- 
advantages arising from inability to handle a cold mixture on 
the street and consequent poor workmanship. 

A Bermudez mixture hardens rapidly at temperatures above 
300° and should not be heated above that point unless provision 
is made for the resulting hardening by making the asphalt cement 
about ten points too soft. The same may be said of those asphalts 



416 THE MODERN ASPHALT PAVEMENT. 

which resemble Bermudez, Mexican, western Venezuelan, and 
the like. The best oil asphalts will resist high temperatures well, 
but mixtures made with them do not require to be very hot, as 
bitumen of this character is so liquid at a comparatively low heat 
that no difficulty is experienced in working them, even the densest, 
at 280°. 

As a general rule, it may be laid down that the following tem- 
peratures may be considered normal on the street: 

Trinidad asphalt: 

Dense mixture 325° F. to 340° F. 

Average " 300° F. " 325° F. 

Open " 280° F. " 300° F. 

Bermudez asphalt: 

All mixtures 280° F. " 300° F. 

The lowest temperature at which a mixture may reach the 
street and still be considered satisfactory is that at which it may 
be raked to a proper grade without too much difficulty. 

The character of a mixture can be judged, to a very considera- 
ble degree, by the appearance of its surface in the truck as it 
comes upon the street, if the haul has extended for any distance, 
and by its cohesion when it is dumped. The best mixture, carry- 
ing plenty of filler, should have, before dumping, a nearly level 
and rather bright surface. If the material stands up in a heap 
as it was dropped from the mixer it is not rich enough. If it 
tumbles to pieces on dumping, it does not contain enough filler. 
The best mixtures, which are the only ones suitable for heavy- 
traffic streets, should stand up and show in part the shape of 
the truck from which they have been dumped. 

This applies, however, only to the natural asphalts. The 
residual asphalts from asphaltic petroleums become so liquid 
at temperatures at which surface mixtures are handled that the 
latter are quite sloppy. 

A load of surface mixture, for the same reasons as in the case 
of binder, only more emphatically so, should be dumped upon 
the binder so far from the material previously raked out that 
it will be possible and necessary to shovel it all over in order to 
get it in place. This is most important, and care in this direction 
is often lacking. If the mixture at the point where the load is 



THE STREET. 417 

dumped is not shovelled over, but merely brought to grade before 
rolling, there will be an excess of mixture at that point which will 
not compress as much under the steam-roller as the neighboring 
surface, with the result that after the street has been subjected 
to traffic for some time that part is higher than the rest. 

The surface mixture is distributed with hot shovels from the 
point where it has been dumped to the place where it is to be 
raked out to the proper thickness for compression. This opera- 
tion should not be conducted too rapidly. No more should be 
spread than the rakers can handle. If it is spread too rapidly 
the rakers will find it necessary to step in it in correcting inequali- 
ties of grade, thus compressing the part where their feet fall. This 
depression they afterward fill with more mixture and therefore 
leave at that point more than there should be. After the street 
is opened for traffic this part of the surface does not yield as much 
to final compression as the remainder and the result is an uneven 
and bumpy grade which is accentuated with the lapse of time 
and aids in the disintegration of the pavement from the blows 
of wheels bounding from the elevated spot to the adjoining sur- 
face. Rakers should on no account be allowed to place their 
feet on the uncompressed surface mixture. If absolute necessity 
arise the depression should not be refilled. 

The mixture after it is spread should be thoroughly raked 
out with rakes having long and strong tines which will penetrate 
through its entire depth. It is necessary, in order to obtain a 
regular surface to the finished street, that all the hot mixture 
shall be broken up to a uniform state of looseness. None of the 
material in the state of compression which it has acquired in the 
truck during the haul to the street should be allowed to remain 
in lumpy form. If lumps remain in the loose hot material the 
effect will be the same as that occurring at the points where the 
rakers place their feet. It is insufficient that the actual surface 
of the loose hot mixture should represent a uniform thickness; it 
must also be of uniform consistency all the way through. 

The lack of perfect form in asphalt surfaces is oftener due 
to this cause than any other, but it is, of course, much empha- 
sized on streets of heavy travel where traffic depresses that part 



418 THE MODERN ASPHALT PAVEMENT. 

containing the least material. With coarse mixtures, and those 
deficient in filler, which do not become so much compressed in 
the trucks, and with mixtures poor in bitumen, results such as 
have been described are not so apt to occur or are brought out 
less under lighter traffic, and, as a matter of fact, with such mix- 
tures it is possible to give a street surface a much prettier original 
finish than can often be obtained with standard mixture which 
carries a high percentage of fine sand, filler and bitumen. 

The raking of the material to a proper grade requires a good 
eye on the part of the workman and proper supervision and a bet- 
ter eye for such work on the part of the foreman. Constant atten- 
tion and great care are, however, the great desiderata. It is 
not difficult to make a good raker out of an inexperienced man 
if he is under good supervision. The great difficulty with all 
rakers is to make them pull out all their material to a loose con- 
dition, especially with a dense mixture such as it is necessary to 
lay on heavily travelled streets. 

The hot mixture having been raked to grade, it was the cus- 
tom, in the early days of the industry when the mixture was more 
loose and open and carried less filler and asphalt cement and 
consequently had less density, to give it its first compression with 
a hand-roller of comparatively light weight. This may be advis- 
able even to-day with similar mixtures. As a rule, however, 
the modern mixture has sufficient density to permit the use of a 
steam-roller at once, and this is the general custom in good prac- 
tice. The hot mixture is, however, allowed to cool to a point 
where it will not be displaced or picked up. To avoid the latter 
difficulty it may be necessary with some mixtures to oil the roller 
with a mixture of kerosene and water, and it is generally found 
to be preferable to run the lighter or guide rolls of the roller on 
the surface first. After the preliminary compression the surface 
is sprinkled with any fine mineral matter which will give it a 
color pleasing to the eye. It is not necessary that this should 
be a hydraulic cement. The excess of dust having been swept off, 
the surface is allowed to cool still further until the roller can go 
on and shape it up without displacing it. Experience can alone 
determine what length of time to allow for cooling. In winter 



THE STREET. 419 1 

it cannot be long, since if a hardened crust is allowed to form by 
the chilling of that portion of the mixture exposed to the air, this 
will have a tendency to break up on further rolling, and fail to 
make a bond with the main mass, resulting in subsequent scaling. 

The aspect of the finished pavement, especially after it has 
been subjected to traffic for a year or two, will depend as much 
on the way it was rolled as on the way the mixture has been raked 
out. The management of a steam-roller requires experience, 
skill, and judgment. The roller if not run with great regularity 
and stopped with care at the end of a run will readily displace 
the surface so that it cannot be easily brought back into form 
again. The first rolling should be with the length of the street. 
It should then be rolled diagonally where this is possible as soon 
as it is evident to the roller engineer that nothing is being accom- 
plished in the original direction. No rule can be laid down as 
to the length of time necessary for rolling a given area of surface. 
The time will depend very much on the season of the year and 
more on the character of the mixture. The hot surface mixture 
will cool more rapidly in the autumn, and cannot be rolled for 
the same length of time as in summer, or at least with any effect. 
Mushy mixtures, where the local sands make mixtures of this 
description, should not be rolled too much. This would injure 
them by breaking the bond in the cool mixture. Mixtures on a 
weak base cannot be rolled to the same extent as those on one 
that is firm. Certain mixtures which are readily displaced may 
require a final shaping up with a roller of wider tread than that 
used for the original compression, one of ten or eleven tons weight 
and tread. This is by no means always necessary if the roller 
engineer is skilful and the mixture a good one; although the weight 
per inch tread is greater in one case than in the other. Follow- 
ing are some determinations of the pressure per inch run for 
various rollers. See table on page 420. 

All rollers are not equally suited for the work. Some are 
strikingly defective in that they are not well balanced. The 
side carrying the motive power is much heavier than the other, 
and the result is that the roller sways, especially when it meets 
an elevation or depression, thus producing a wavy surface. The 



420 



THE MODERN ASPHALT PAVEMENT. 



ROLLERS— PRESSURE PER INCH RUN. 

IROQUOIS IRON WORKS. 



Size of roller 

Duplex engine 

Main roll, width of tire. 
Pressure per linear inch 



2} tons 

4X5 
30 ins. 
125 lbs. 



5 tons 

6X6 
38 ins. 
210 lbs. 



8 tons 

7X7 
48 ins. 
250 lbs. 



13 tons 

8XL0 

60 ins. 

300 lbs. 



best type of modern roller has a compensating weight attached 
to the channel iron on the side opposite to that carrying the motive 
power. Whether a roller is properly balanced or not can be deter- 
mined by running it on a scantling so that the latter is exactly 
in the middle of the rolls and then noting whether it has a ten- 
dency to tip toward the side carrying the motive power. If 
it does it should be balanced by bolting a weight to the channel 
iron on the side which is too light. 

Rollers should be provided with a steering-gear which can 
be controlled by power, thus enabling the engineer to give his 
undivided attention to the street. Such rollers are available. 
Throttle-valves should be of a kind which permit the gradual 
reduction of speed. 

The importance of having a perfect roller, if good work is to 
be done, should not be overlooked. That offered by the Iroquois 
Iron Works, Buffalo, N. Y., is the best balanced and most care- 
fully constructed roller with which the author is acquainted. It 
is illustrated in Fig. 23. 

These rollers are made of various sizes, 2\, 5, 8, and 13 tons, 
the latter being used for rolling the base and for finally shaping 
the asphalt surface where mixture requires it after previous com- 
pression with a lighter roller. Such shaping is only necessary 
when the mixture is of a mushy nature and consequently some- 
what displaced by the roller of narrower tread. 

Work Under Particular Condition. — In the preceding para- 
graphs consideration has been given only to what may be called 
straight work; that is to say, the laying of an extended area where 
everything connected with the work goes on in a perfectly nor- 
mal way. This, however, is not the only kind that is met. There 



422 THE MODERN ASPHALT PAVEMENT. 

are joints to be made, between the work of different days, with 
the curb and with headers, around boxes, manholes, and similar 
protuberances, and with railway tracks or the brick or stone 
stretchers along them. It is also quite possible, owing to unavoid- 
able circumstances, that the surface may be found to be, after 
its preliminary compression, too high at one point — in the gutter 
for example — or too low at another. Owing to chilling of the 
surface it may not close up properly or from inaccessibility to 
the roller fail to be sufficiently compressed. These conditions 
must be met and the defects remedied, all in their own way, and 
in many cases tools especially provided for the purpose, known 
as tampers and smoothers, must be used. These tools are shown 
with some others in the accompanying illustration, from the cata- 
logue of the Iroquois Iron Works of Buffalo, N. Y. Fig. 24. 

The tampers and smoothers must be used with great care and 
should not be too hot. If the smoothers are hot and it is difficult 
to tell their temperature in bright sunshine, they may do much 
damage by hardening the bitumen in the surface, and their use 
is only advisable in very skilful hands. They are a relic of the 
days when mixtures were used which would not close up readily 
on account of poor grading and deficiency in bitumen. With 
standard mixture they are seldom necessary except on joints. 
The tampers are not as dangerous, since they are not left in 
contact with the surface as long as the smoothers. They are 
used on joints, around manholes, and along rails at points 
which the roller cannot reach and in reducing inequalities in the 
gutter. 

Attempts to reduce projections above the proper grade with 
tampers are rarely successful; the material at the point is merely 
more strongly compressed than that in the immediate neighbor- 
hood, with the result that the latter goes down under traffic and 
the original elevation is brought out again. Especially in gutters, 
where the surface is too high, the excess should be removed with 
a hot shovel, if necessary, after heating it with a smoothing iron. 
Except on joints between days' work, the use of tampers and 
smoothers is a makeshift to cover up poor raking, and the best street 
foreman will be the man who finds the least necessity for their 



424 THE MODERN ASPHALT PAVEMENT. 

use, especially that of the smoothers, for reasons which have been 
already mentioned. 

Joints between different days 7 work, according to the prefer- 
ence of the street foreman, are made in different ways. Usually 
the mixture is compressed to a feather-edge under the steam- 
roller and left in this condition. On the following morning the 
feather-edge is cut back to a point where the full thickness of 
surface is shown. This edge is painted with melted asphalt and 
the joint between the two days 7 work is made in this way. 

In the middle West an excellent joint is made by imbedding 
in the soft material, while still hot and after it has been raked 
off to a feather-edge, a rope of about f of an inch in diameter 
to which a flap of canvas is attached. The steam-roller is run 
over this until final compression is obtained, and on the following 
day the rope and canvas are easily detached, leaving an excellent 
section to work to without the necessity of cutting back and 
losing good material. This form of joint is to be recommended. 

SUMMARY. 

The preceding chapter describes the method of transporting 
and handling on the street the surface mixture, together with 
the use of the tools employed in laying it. 



PART VI. 

THE PHYSICAL PROPERTIES OF ASPHALT SUR- 
FACES. 



CHAPTER XXI. 

RADIATION, EXPANSION, CONTRACTION, AND RESISTANCE TO 

IMPACT. 

The physical properties of asphalt pavements are of interest 
in two ways : first, from a general point of view as pertaining to 
asphalt surfaces as a whole, and, second, the peculiar character- 
istics which are dependent on particular mixtures according as 
they differ in sand grading, the amount and character of filler 
they contain, and the consistency and character of the cementing 
material with which they are bonded. 

Radiation from Asphalt Pavements. — Asphalt pavements have 
been frequently criticised because of their great absorption of heat 
when exposed to summer suns in an atmosphere of high tem- 
perature and its radiation again during the ensuing night. With a 
view of determining the number of thermal units of heat thus 
absorbed and radiated numerous inquiries have been addressed 
to the author as to the specific heat of asphalt. It has been 
assumed that the specific heat of asphalt could not be very differ- 
ent from that of other native bitumens the records of which are 
available. For example, the specific heat of petroleum is given 
by Pagliani 1 as .498 to .511. It must be remembered, how- 

1 Atti di Torino, 1881, 17, 97. 

425 



426 THE MODERN ASPHALT PAVEMENT. 

ever, that but 10 to 11 per cent of an asphalt surface consists of 
bitumen; the remainder is quartz and mineral matter which has a 
specific heat no greater than .201. The specific heat of an asphalt- 
surface mixture cannot, therefore, be much greater than that of a 
granite pavement, or be the cause of any great difference in its 
temperature. That the asphalt pavement seems hotter must be 
due to other causes, and this is to be attributed to the fact that 
having a blacker surface it absorbs heat rather more rapidly than 
the granite and radiates it much more rapidly after sunset. There 
is, therefore, not much more heat given out by asphalt than by 
granite pavement, but since it may be given out more rapidly 
it may be more noticeable. Each form will give up about the 
same quantity during the entire night. 

That the figures assumed for the specific heat of asphalt are 
not far out of the way may be seen from the following informa- 
tion furnished in " Municipal Engineering " J by Mr. A. W. Dow. 



SPECIFIC HEAT. 

Refined Trinidad asphalt 350 

Cuban asphalt cement 401 

Trinidad " " 381 

Bermudez " " 413 

Maracaibo " " 447 

Quartz sand 201 

Maracaibo and Bermudez asphalts, being nearly pure bitu- 
men, afford the best idea of the true specific heat of asphalt. 
This factor is somewhat smaller than that for petroleum oil, and 
this is evidently due to the presence of more condensed molecules 
in the asphalt than in the oil. 2 

Some experiments conducted in the summer of 1907 with 
cylinders of granite, brick and asphalt surfaces, confirmed the 
previous conclusions, as will be seen from the following data: 

1 1904, July, 27, 22. 

2 Additional data in regard to the specific heat of mineral oils will 
also be found in "Petroleum," Berlin, 2, 521, April 3, 1907. 



RADIATION, EXPANSION, ETC. 



427 



ABSORPTION AND RADIATION OF HEAT BY VARIOUS 
PAVEMENTS. 

May, 1907. 



Time. 


Granite. 


Brick. 


Asphalt. 


Thermom. 
Temp. 


Gain or 
Loss. 


Thermom. 
Temp. 


Gain or 
Loss. 


Thermom. 
Temp. 


Gain or 
Loss. 


10.30 


72.0" 

93.2 

102.2 

98.6 
84.2 




73.4 

93.2 

101.3 

101.3 

86.0 




72.0 
91.4 

100.4 

100.4 

86.0 




11.30 

12.30 

3.00 

4.00 


+ 21.2 
+ 30.2 

- 4.6 

- 18.0 


+ 19.8 
+ 27.9 
+ 27.9 
- 15.3 


+ 19.4 
+ 28.4 
+ 28.4 
- 14.4 



June, 1907. 



11.05 

11.35 

12.05 

2.35 

3.05 

4.05 



80.6 

88.0 




80.6 
90.6 




78.8 
89.6 


+ 7.4 


+ 10.0 


91.5 


+ 10.9 


93.2 


+ 12.6 


92.0 


92.8 


+ 12.2 


93.6 


+ 13.0 


91.4 


87.8 


- 5.0 


89.4 


- 4.2 


87.8 


84.2 


- 8.6 


84.2 


- 9.4 


84.2 



June, 1907. 



+ 10.8 
+ 13.2 

+ 12.6 

- 3.6 

- 7.2 



11.15 


81.5 
89.6 




83.4 
93.1 




82.4 
93.1 




11.45 


+ 8.1 


+ 9.7 


+ 10.7 


12.05 


93.0 


+ 11.5 


96.8 


+ 13.4 


96.8 


+ 14.4 


2.05 


103.8 


+ 22.3 


105.8 


+ 22.4 


105.8 


+ 23.4 


3.15 


93.0 


- 10.8 


93.2 


- 12.6 


91.4 


- 14.4 


4.30 


86.0 


- 17.8 


85.2 


- 20.6 


84.2 


- 21.6 



Black bulb thermometer in each case 90° F. to 98° F. in sun. 
Air temperature, May, 73° F. to 84° F. 

June, 81° F. to 92° F. and 81° F. to 93° F. 
Clearer atmosphere on second day. 

Expansion and Contraction of an Asphalt Surface. — Asphalt 
surfaces necessarily expand and contract with changes of tem- 
perature. As they consist very largely, to the extent of about 
89 per cent, 'of mineral matter, this expansion must be closely 
that of quartz, of which the mineral aggregate is principally com- 
posed and must be fairly constant for all surfaces. Whether the 
cementing material is sufficiently strong to yield to such con- 



428 THE MODERN ASPHALT PAVEMENT. 

traction without the fracture will determine whether the pave- 
ment cracks or not. It is, of course, a feature which will vary 
with the character of every mixture, depending upon its com- 
position. This subject will be taken up in detail in a succeeding 
chapter, where the cause of cracks in pavements is considered. 1 

Impact Tests of Asphalt-surface Mixture. — The force which 
has the greatest tendency to injure an asphalt surface is that of 
impact. The blows from horses' hoofs or from the wheels of 
vehicles where the surface is irregular deteriorates it to a much 
larger extent than attrition or ordinary travel. A well-con- 
structed asphalt surface has been known to carry without injury 
a load of 51 tons on a truck with broad tires, whereas the same 
pavement under constant impact would deteriorate perceptibly 
in the course of years. 

The capacity of any asphalt surface to resist impact can be 
readily tested in the laboratory with appropriate testing 
machines, such as that devised by Mr. Logan Waller Page, 
of the Office of Public Roads, and described on page 34 
of Bulletin No. 79 of the Bureau of Chemistry, and which 
is illustrated in Fig. 25. Cylindrical test-pieces are made 
from the surface mixture to be examined in a mold which permits 
of its being filled with the hot mixture at an appropriate tem- 
perature and of being compressed by means of blows with a ham- 
mer of four pounds weight, ten of which are given to each end 
of the cylinder. These cylinders are usually made 1.25 inches 
in diameter and 1 inch high, and weigh about 50 grams. When 
brought under the impact machine they are held firmly with a 
plunger resting on the surface with a spherical bearing having a 
radius of 4/10 of an inch. The hammer is then allowed to drop 
from a distance of 1 cm., and this distance is increased by this 
amount at each blow until the test-piece yields. Under these 
conditions tests have shown that the resistance of any asphalt 
surface to impact will depend upon: 

1. The sand grading. 

2. The character of the sand. 

1 See page 480. 



RADIATION, EXPANSION, ETC 



429 



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Fig. 25. — Instrument for Impact Test. 



430 



THE MODERN ASPHALT PAVEMENT. 





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THE MODERN ASPHALT PAVEMENT. 





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RADIATION, EXPANSION, ETC. 



433 



3. The amount of filler present. 

4. The character of the asphalt in use. 

5. The consistency of the asphalt. 

6. The density and degree of compaction of the test-piece. 

7. The percentage of bitumen in the mixture. 

The data in the preceding tables will illustrate the application 
of the test. 

From these results it appears that the old-time mixtures which 
are low in bitumen, those from Minneapolis and Rochester, do not 
withstand impact to nearly the extent that the more modern 
mixtures do, and reveal the cause of the inferiority of the pave- 
ments constructed with such mixtures. 

The results of tests by impact at different temperatures of 
the standard New York mixture made with various asphalts 
show that those in which Trinidad lake asphalt is the cementing 
material give a much greater resistance to impact at low and 
medium temperatures, and are much less affected by tempera- 
ture changes than those made with Bermudez asphalt, while the 
variation in the character and grading of the sand, and the per- 
centage of filler and of bitumen, are made evident by other data 
in the table. 

It should also be observed that the work done in fracturing 
the test-pieces is relatively as the square of the number of blows. 

The impact test is also valuable in revealing the difference in 
susceptibility to water action of different mixtures. Cylinders 
of standard Trinidad and Bermudez asphalt mixtures were pre- 
pared and some of them tested by impact at 78° Fahr. as soon as 
made. Others were immersed in water for three months and the 





Trinidad. 


Bermudez. 


Density 


2.24 

21 
20 

.129 


2.24 

16 
13 

.157 


Number of blows: 

Original material 


After three months' exposure 
to running water 

Water absorbed : 

Pounds per square yard 



434 THE MODERN ASPHALT PAVEMENT. 

amount absorbed determined, after which they were subjected to 
the impact test. The results are shown in the table at bottom of 
page 433. 

It is readily seen that the Bermudez mixture is much more 
weakened by immersion in water than that made of Trinidad 
asphalt. The value of the impact test is, therefore, assured from 
the results thus far obtained and the investigation of the subject 
will be carried out in greater detail in the future. 

SUMMARY. 

In the preceding pages the question of the radiation of heat 
from asphalt pavements, their expansion and contraction, and 
resistance of various asphalt surface mixtures to impact axe 
considered. 



PART VII. 

SPECIFICATIONS FOR AND MERITS OF ASPHALT 
PAVEMENTS. 



CHAPTER XXII. 

SPECIFICATIONS. 

As has already been mentioned, the specifications for the con- 
struction of asphalt pavements which are prepared by engineers 
who are not thoroughly acquainted with the subject are often 
wanting in some respects or make certain requirements which 
are undesirable, unessential, or unnecessarily increase the cost of 
the pavement. For the construction of an asphalt pavement 
which is to meet the requirements of ordinary traffic in a majority 
of our cities the following, in the author's opinion, will be found 
to be a thorough protection of the city's interests, and not open 
to objection by the bidders that the provisions are unreasonable. 

Specifications for Asphalt Pavement on Portland-cement 
Concrete Foundation. 1 

Extent of Work, — The work shall consist of regulating and 
grading the entire street, constructing combined curb and gutter, 
laying asphalt pavement, and all work incidental thereto, all in 
accordance with the following specifications: 

Removal of Old Materials, — All old material which is not to 
be used in the work, shall become the property of the contractor 
and be removed by him. 

1 As an example of the type of specifications in actual use in cities, those 
portions of the specifications of Kansas City, Mo., which apply to the tech- 
nical portion of the work are presented in an appendix. 

435 



436 THE MODERN ASPHALT PAVEMENT. 



Grading. 

Excavation, Grading and Preparation of Foundation. — Any- 
old material to be used again shall be compactly piled on the side 
of the roadway. The excavation shall be carried to the grade 
established by the Engineer. When completed, the sub-grade 
shall present a line and contour parallel with and approximately 
„ . . .inches below the surface of the finished pavement to be con- 
structed. Should any soft, spongy, vegetable or other objection- 
able matter be disclosed by the excavation thus made, or be 
located where filling is to be done, such material shall be removed 
and replaced with suitable material, which shall be thoroughly 
compacted. Whenever deemed necessary by the Engineer, the 
sub-grade shall be rolled with a suitable steam roller. 

Inspection and Piling of Material. — The materials for con- 
struction, when brought upon the street, shall be neatly piled 
so as to present as little obstruction as possible to travel. No 
material shall be used without the approval of the Engineer, the 
contractor furnishing all labor necessary for inspection, without 
&ny charge. 

Filling and Embankments. — Embankments shall be brought 
up to the designated grades, and the top shaped off and compacted 
as defined for earth excavation. Such excavated material as 
may be fit for the purpose and as may be necessary, shall be used 
io fill in those parts of the streets which are below the aforesaid 
grades. 

Concrete. 

Upon the sub-grade, prepared as above described, Portland- 
cement concrete composed of Portland cement, clean sharp sand, 
and broken stone or slag, will be laid to an average thickness of 

inches. Suitable gravel may be used in combination with 

the stone or slag, as hereinafter provided. The cement shall be 
of the best quality of American manufacture and shall be sub- 
mitted to the Engineer for inspection at least ten (10) days before 
it is used. It shall conform to the following tests, conducted 



SPECIFICATIONS. 437 

according to the methods recommended by the Committee on 
Uniform Tests of Cement of the Am. Soc. of C. E. It shall not 
set in less than one (1) hour. When mixed in the proportion of 
one (1) part of cement, by weight, and three (3) parts of standard 
sand, it shall have a tensile strength aftex exposure of one (1) 
day in air and six (6) days in water of at least one hundred and 
fifty (150) pounds. ' 

The sand shall be clean and sharp, not more than 20 per cent 
of which shall pass a 50-mesh screen. It shall be free from loam 
adherent to the sand grains. The gravel shall be of such size 
that it will satisfactorily fill the voids in the broken stone, and 
it shall not contain dirt or foreign matter. The broken stone 
shall consist of granite, trap, or other hard rock or slag which shall 
be satisfactory to the Engineer. It shall be of such a size that 
all will pass through a revolving screen, having holes two and one- 
half (2J) inches in diameter, and be retained by a screen having 
holes one-half (J) inch in diameter. Stone which is the run of the 
crusher may be used when provision is made for the consideration 
of finer particles than one-half (J) inch which it contains as sand. 
The unit of measure in mixing these materials will be the barrel 
of cement, weighing 380 pounds, and four (4) cubic feet for sand, 
gravel, and stone. They shall be mixed in the following propor- 
tions and in the following manner: 

The sand and cement shall be mixed dry in the proportion by 
volume of one (1) of cement to three (3) of sand, and then made 
into a mortar by the addition of water. To this mortar will 
be added six (6) measures of wet broken stone, and the whole 
thoroughly mixed by hand or machinery until it is entirely uni- 
form. 

Where gravel is available this may be used in such proportion 
that the gravel will fill the voids in the broken stone, with a con- 
sequent decrease in the amount of mortar necessary to make a 
compact concrete. For example: A one (1) to three (3) mortar 
which could be mixed with only six (6) parts of broken stone 
may be mixed with a combination of two (2) to three (3) parts 
of gravel and four (4) to six (6) parts of broken stone. The con- 
crete thus mixed will be of such a consistency, owing to the per- 



438 THE MODERN ASPHALT PAVEMENT. 

centage of water which it contains, that it shall quake very slightly 
when thoroughly rammed. 

The concrete as thus prepared shall then be spread on the 
sub-grade and rammed, the surface being so graded that in its 
finished condition it shall average .... inches below that of the 
finished pavement. No concrete shall be used that has been 
mixed more than one hour. 

The concrete, after laying, shall be properly protected and 
the surface shall be kept moist in warm weather by sprinkling 
at proper intervals. 

At the expiration of such a period as is found to be necessary 
in order that the concrete shall have attained a sufficient set to 
sustain a steam roller, the binder course shall be laid. 

Asphalt Pavement. 

Definition. — The pavement proper shall consist of a binder 
course. . . .inches in thickness and a wearing surface. . . .inches 
in thickness, equal in composition to the pavement mixture here- 
inafter described. 

Binder Course. 

The alternative of an open or close binder course is given. 
In any specification but one should be called for. The close 
binder course is much more desirable. 

Open Binder. — Stone. — The binder shall be composed of 
suitable clean broken stone passing a one and a quarter (1|) 
inch screen. 

Asphaltic Cement. — The stone shall be heated in suitable 
appliances, not higher than 300° Fahrenheit, and then thoroughly 
mixed by machinery with asphaltic cement equivalent in com- 
position to that hereinafter set forth, in such proportion as will 
cover the stone with a glossy coat and without any excess of 
asphaltic cement. 

Laying. — The binder must be hauled to the work and spread 
while hot upon the foundation to such thickness that, after 
being immediately compacted by rolling, its average depth 
shall be. . . .inches, and its upper surface shall be approximately 



SPECIFICATIONS. 439 

parallel to the surface of the pavement to be laid. Upon this 
binder course shall be laid the wearing surface. 

No traffic, except such as may be required in depositing the 
surface mixture or in otherwise prosecuting the work, shall be 
allowed on the binder course. 

Compact or Close Binder. — Compact or close binder shall 
be composed of hard, clean broken stone which shall pass an 
opening one (1) inch in diameter, the voids in which are filled 
with finer stone passing an opening three-eights (§) inch in diameter, 
while the voids in the mixed stone shall be filled with a well 
graded sand or old asphalt surface mixture which has previously 
been in use, and which has been softened by heating so as to allow 
it to be incorporated properly with the stone. If sand is used, 
sufficient asphalt cement shall be added to thoroughly coat the 
mineral aggregate with bitumen without showing any excess on 
compression with a hot tamper, while if old surface material is 
used, sufficient cement shall be used to coat the stone and produce 
the same result. 

Care should be exercised with close binder that it does not 
carry an excess of fine material or of asphalt cement, as in this 
case the wearing surface of the pavement may have a tendency 
to displacement. . 

Asphaltic Cement. — The asphaltic cement for the binder 
course should have a consistency of at least twenty (20) points, 
as indicated by the Bowen machine, higher than that in use 
in the surface. 

Pavement Mixture. — The pavement mixture for the wearing 
surface shall be composed of: 

(a) Asphaltic cement (Refined asphalt and flux). 

(6) Sand of satisfactory grading and grain. 

(c) Filler, consisting of finely powdered mineral matter. 

Asphaltic Cement. — The asphaltic cement shall be composed 
of refined asphalt and flux of such character that the bitumen,, 
without regard to the mineral matter present, shall be a homo- 
geneous solution, and present the following characteristics: 

1. The proportion of bitumen soluble in 88-degree naphtha 



440 THE MODERN ASPHALT PAVEMENT. 

shall not exceed seventy-eight (78) per cent, nor fall below sixty- 
four (64) per cent. 

2. A No. 2 needle, weighted with one hundred (100) grams, 
shall penetrate, in five (5) seconds, at 78° F., a distance of from 
three (3) to nine (9) millimeters. 

3. When twenty (20) grams are heated in a receptacle about 
two and a half (2^) inches in diameter and about two (2) inches 
high, for seven (7) hours, in an oven maintained at a uniform 
temperature of about 325° F., as determined by a thermometer, 
the bulb of which is immersed in a similar receptacle filled with 
oil, it shall not lose more than four (4) per cent. Its flash point 
as determined in a New York State closed oil tester, shall not 
be less than 350° F. 

4. Ninety-five (95) per cent shall be soluble in carbon disulphide 
at air temperature, and not more than one and a half (1J) per cent 
of the bitumen shall be less soluble in carbon tetrachloride than 
in carbon disulphide, the test for the former being conducted 
by submitting the bitumen to the action of the tetrachloride 
for twenty-four (24) hours before filtration. 

Sand. — The sand shall consist of hard grains, not necessarily 
sharp, but not containing more than one (1) per cent of clay 
or loam. On sifting, the entire amount shall pass a ten (10) 
mesh screen, at least fifteen (15) per cent shall pass an eighty 
(80) mesh screen, and seven (7) per cent a one-hundred (100) 
mesh screen. 

Filler. — 1. Powdered Mineral Matter or Dust — The filler 
shall consist of ground limestone or any other mineral matter 
of sufficient density to produce a powder having a volume weight 
of at least ninety (90) pounds to the cubic foot. It shall be so 
fine that at least sixty-six (66) per cent shall pass a two-hundred 
{200) mesh screen, and all of it shall pass a fifty (50) mesh screen, 
-while, when thoroughly agitated with distilled water at a tem- 
perature of 68° F., by means of an air blast, avoiding cyclonic 
effects, not more than forty (40) per cent shall subside on standing 
for fifteen (15) seconds. 

2. Portland Cement. — The filler shall consist of Portland 



SPECIFICATIONS. 44 1 

cement of such a degree of fineness that seventy-five (75) per cent 
will pass a two-hundred (200) mesh sieve. 

Only one or the other of the materials described as filler should 
be called for in any specification, as the difference in cost between 
the two is sufficient to require a separate estimate on each. 

Combining Materials. — The materials complying with the 
above specifications shall be mixed in proportions by weight, 
depending upon their character. The percentage of matter soluble 
in carbon disulphide in any pavement mixture shall be not less 
than 9.5 nor more than 12.0 per cent. 

The sand and the asphaltic cement will be heated separately 
to such temperatures that the finished mixture shall, depending 
on the asphalt in use, have a temperature of from 290° to 
330° Fahr. The filler shall be mixed, while cold, with the hot 
sand. The asphaltic cement will then be mixed with the sand 
and stone dust, at the required temperature and in the proper 
proportion in a suitable apparatus, so as to effect a thoroughly 
homogeneous mixture. 

Laying the Pavement. — The above mixture shall be hauled 
to the street in trucks properly protected from radiation by 
tarpaulins at a temperature of not less than 250° Fahr., and spread 
upon the binder to such a depth as will insure an average thick- 
ness of ... . inches after ultimate compression. This compression 
will be attained by first smoothing the surface with a hand-roller, 
or light steam-roller, after which hydraulic cement or stone dust 
shall be swept over it, when the rolling will be continued with a 
steam-roller until the surface is properly compacted. 



Bituminous Concrete Pavement. 

For a bituminous concrete surface, the character of the asphalt 
cement, sand, filler and stone will be the same as those provided 
for in the previous specifications. 

Determination of Proportions. — The wearing surface mixture 
shall be composed of the materials previously specified combined 
in proportions to be determined as follows: 

The stone shall be separated into fragments which are retained 



442 THE MODERN ASPHALT PAVEMENT. 

and those which pass a screen with circular openings of three- 
eighths (|) inch size. While hot, a layer of the coarser fragments 
are to be spread on the bottom of a strong box exactly one foot 
square and shaken down. Hot fragments of the smaller size 
are then shaken into the voids in the larger stone until the latter 
are filled. Into this mixture hot sand and filler, in the proportion 
of ninety (90) per cent sand and ten (10) per cent filler, are sifted, 
with continued jolting and jarring of the box, until the stone has 
taken up all of the fine material possible. This operation is 
repeated with subsequent layers until the box is full. It is then 
struck off evenly and weighed. The total weight of the mineral 
matter in the box obtained in this way is divided by the weight 
of a solid cubic foot of mineral matter of the same density, and 
the voids in the mixture of rock, sand and filler determined. The 
voids should not exceed 25 per cent. 

The proportions by weight in which the different components 
are present is then determined either by screening the contents 
of the box or by originally taking a definite amount of each and 
determining by difference the amount actually placed in the box. 
These proportions shall be those which shall be subsequently used 
in making up the mineral aggregate for the surface mixture 
unless observation on the street in laying the mixture should 
indicate the necessity for increasing the amount of fine material 
present. 

The proportions will ordinarily vary between the following 
limits: 

Coarse stone 56 to 30% 

Fine stone 16" 26 

Sand 25 " 33 

Filler 3" 5 

The variations will depend upon the shape of the fragments 
of the coarse stone and on the uniformity in size of the fragments 
of the two dimensions. 

The amount of bituminous cement necessary to coat the 
particles of the above mineral aggregate and fill the voids therein 
as nearly as possible, shall be determined as follows: 



SPECIFICATIONS. 443 

To the hot mineral aggregate assembled in the proportions 
arrived at as above, shall be added the bituminous cement in 
an amount which previous experience points out as within the 
limits for such a mixture. After thorough mixing the material 
prepared in this way is placed upon a firm surface (such as one 
of hydraulic concrete) and compacted with a hot tamper until 
it is thoroughly compressed. If bitumen comes to the surface 
to a slight extent, the amount used is satisfactory, but if it appears 
in excess, the amount of bituminous cement must be diminished, 
or, if it appears dry, it must be increased until the proper appear- 
ance is obtained. The percentage thus determined will be followed 
in making the surface for the street, but it may be modified to 
a certain extent to correspond to unavoidable variations in the 
mineral aggregate, but in no case shall it exceed 8.0 per cent, 
nor fall below 6.5 per cent. 

Preparation and Mixing of Bituminous Wearing Surface. — 
The sand and stone shall be heated in suitable heaters to the re- 
quired temperature, which temperature shall be dependent upon 
that of the atmosphere at the time the mixing is in progress, and 
upon the character of the bituminous cement in use. These 
materials, while in this heated condition, shall be separated into 
not less than three sizes by passing over a screen having perfora- 
tions or openings of at least two diameters, so arranged as to 
separate the stone and sand into particles larger than three-eighths 
(|) inch in their greatest diameter, particles passing a screen 
with openings three-eighths (|) in size and retained on a 10-mesh 
screen, and particles passing the latter screen; the material of 
each size being collected separately in suitable bins. The material 
of each size shall then be weighed or measured out in the proportions 
determined upon, together with a proper proportion of filler 
(finely ground mineral matter) not previously heated. The 
aggregate shall then be mixed with the bituminous cement, pre- 
pared as described in the paragraph on this material above given, 
in a suitable mixing appliance, either pans or a double-bladed 
revolving mixer of the type generally used in the preparation of 
bituminous paving mixtures, the operation of mixing to be con- 
tinued until uniformity is attained. 



444 THE MODERN ASPHALT PAVEMENT. 

Laying Bituminous Wearing Surface. — In this condition the 
bituminous wearing surface mixture shall be hauled to the street 
in suitable carts or wagons, properly protected from the weather, 
so as to prevent an undue loss in temperature. It shall be spread 
upon the foundation with hot rakes to such a depth that after 
receiving its ultimate compression by rolling with a steam roller, 
it will have an average thickness of two (2) inches. 

Surface Finish. — After the rolling of the bituminous wearing 
surface has been completed, there shall be spread over it a thin 
coating of quick-drying bituminous flush-coat composition, 
specially prepared, the purpose of this coating being to thoroughly 
fill and smooth out any unevenness which may be on the surface 
of the coarser mixture. 

There shall then be spread over and rolled into the wearing 
surface a thin layer of coarse sand or stone chips for the purpose 
of presenting a gritty surface, which shall not be slippery. The 
character and size of the sand or stone chips to be spread upon the 
surface, and the consequent degree of roughness of surface, shall 
be determined by the Engineer, who may, at his discretion, 
omit the use of stone chips and substitute therefor a light sweep- 
ing of hydraulic cement, stone dust, or similar material, in order 
to secure a smoother surface. 



Material for Repairs. 

Repairs. — In case of repairs, it shall be required that such 
repairs be made with a pavement mixture equal to the above 
described. 

Clearing Up. 
All surplus materials, earth, sand, rubbish, and stones are to 
be removed from the line of the work. All material covering thft 
pavement and sidewalks shall be swept into heaps and imme' 
diately removed from the line of the work. 



SPECIFICATIONS. 445 

Maintenance. 

Contractor to Make Repairs. — The contractor shall make all 
repairs which may be necessary during a period of . . . .years 1 
from the date of acceptance of the pavement, which are caused 
by improper construction due to defective materials or workman- 
ship, and he guarantees that he will repair during this period, 
any and all defects arising through its usual use as a roadway. 
In case of the contractor's failure or neglect to do so within thirty 
days after notification by the duly authorized official, such notice 
to be served upon him in writing, either personally or by leaving 
said notice at his place of business or with his agent in charge 
of the work, the said duly authorized official may repair, or cause 
such defects to be repaired, and may recover cost thereof from 
the contractor or his sureties. 

Temporary- Repairs in Winter. — The contractor shall have 
the right, in case of trenches, to provide against settlement by 
covering the surface of the cut with broken stones and maintain- 
ing the surface for a sufficient period, and during winter weather 
any hole in the pavement may be filled and maintained with 
binder, asphalt mastic, or other suitable material. 

Repairs to Openings. — During the period of maintenance, 
the contractor shall, within thirty (30) days after the receipt 
of notice so to do, restore the pavement over all openings made 
under permits legally issued by the duly authorized official for 
new service connections, or repairing, renewing, or removing 
the same, and over all trenches made for carrying sewers, 
water or gas pipes or any other sub-surface pipes or conduits, 
for the sum of $3.50 per square yard for any opening less than 

1 The author has suggested no definite period of guaranty as there is a 
tendency on the part of the larger cities to shorten this to a very consider- 
able extent, New York, Chicago, Philadelphia, and St. Louis now calling 
for five years, while in the State of California no guaranty whatever is 
required. Shorter periods are called for in view of the fact that municipal 
officials are now in a position to judge of the character of the work that is 
being done on any contract before acceptance, which was not the case 
years ago. 



446 THE MODERN ASPHALT PAVEMENT. 

ten (10) square yards in area, and $3.00 per square yard over any 
trench measuring more than ten (10) square yards in area; $3.25 
per square yard for restoring the pavement over any opening 
between or alongside of surface railroad tracks which shall exceed 
ten (10) square yards in area, and in case of any injury to the 
surface of the pavement caused by fire or accident, same shall be 
replaced for the sum of $2.00 per square yard. The concrete 
foundation, if relaid, shall be of the same thickness as that origi- 
nally laid. The contractor will not be held responsible, during 
the period of guaranty, for any defects in the pavement or mate- 
rials, which may have been caused by the opening of trenches 
or by the improper backfilling of the same, and will not be com- 
pelled to do the repaving over said trenches, except as herein- 
before provided, nor shall he be held responsible for deterioration 
of the pavement along the rails of street railway tracks, if the 
form of construction is such that the rail vibrates under the traffic 
it carries, unless the track construction has been in charge of the 
contractor himself, nor shall he be obliged to replace cracks in 
the surface, unless they have resulted in the disintegration of 
the surface. 



Cement Curb and Gutter. 

Cement curb and gutter shall be composed of concrete formed 
as follows: 

One (1) part of Portland cement. 

Three (3) parts of clean sharp sand, or other suitable material. 

Five (5) parts of crushed stone. 

Cement and Sand. — Cement and sand shall be equal to the 
materials hereinbefore described for use in concrete foundation. 

Stone. — The crushed stone shall be clean, free from dirt, and 
crushed to such size as to measure not more than one (1) inch in 
any dimension. It shall be deposited at the site of the work in 
such manner as to insure its cleanliness. 

Foundation. — The curb and gutter composed of the above 
materials shall rest on a foundation of cinders six (6) inches in 
thickness after being thoroughly compacted by ramming. 



SPECIFICATIONS. 447 

Dimensions. — The gutter flag shall be eighteen (18) inches 
wide and five (5) inches thick; the curb shall be six (6) inches 
thick throughout, except at the upper face corner, which is to 
be rounded to a radius of one and one-half (1£) inches. The 

height of the curb above the gutter flag shall be inches, all 

as shown on plans. 

Finish. — All exposed surfaces shall be covered with a finish- 
ing coat of mortar three-eighths (f) inches in thickness, composed 
of one (1) part of cement thoroughly mixed with one and one- 
half (H) parts of sand. 

Before the concrete sets, the curb and gutter shall be cut into 
sections not exceeding six (6) feet in length. 

Construction. — The curb and gutter as hereinbefore described 
shall be constructed at the grade and to lines established by the 
Engineer, .... feet from and parallel with the centre line of the 
street, except at intersections of streets and alleys, at which points 
it shall be returned to the street line, the necessary circular sec- 
tions being built to radii established by the Engineer. The curb 
shall be properly back-filled to the top thereof. 

Proposals. 

Bidders will be required to make proposals on blank forms 
furnished by the Engineer, which proposals shall state: 

A price per cubic yard for excavation; 

A price per cubic yard for embankment or filling; 

A price per cubic yard for hauling excavated material or 
material for use in embankment, for each 1000 feet in excess of 
one-half mile; 

A price per lineal foot for straight combined curb and gutter; 

A price per lineal foot for circular combined curb and gutter. 

An inclusive price for asphalt pavement, including foundation, 
open or close binder, and wearing surface, together with main- 
tenance for a period of . . . .years. 1 

1 Attention must be called to the fact that propositions for the use of 
one kind of binder alone and one type of filler alone should be preferably 
specified for any one street. If th^y are both specified, there should be some 
provision for alternative bidding. 



448 THE MODERN ASPHALT PAVEMENT. 

An inclusive price for bituminous concrete pavement, in- 
cluding foundation and a bituminous concrete surface, with 
maintenance for a period of . . . .years. 1 

Other Specifications. — Specifications of another type will be 
found in t,he appendix, those issued by Kansas City being char- 
acterized by demanding an asphalt cement of a certain character 
without regard to the fine material from which it is made, and are, on 
this account, much to be recommended from many points of view. 

Clay Soils in Cold Climates. — Although the preceding speci- 
fications are, as has been said, satisfactory in the majority of 
instances there are cases where, owing to the character of the 
climate, sub-soil, or heavy traffic to be carried by the pavement, 
special provisions must be made. On clay sub-soil in cold climates 
some special provisions, such as are made in Manitoba, may be 
desirable in the treatment of the sub-soil base. Such a provision 
may be outlined as follows : 

In clay soils trenches shall be dug across the line of the street 
from the centre to the trenches in which the curb is laid on each 
side of the street, to a depth of six (6) inches and filled with broken 
stone or large gravel. The entire roadbed will then be thor- 
oughly rolled with a steam roller, having a tread of at least (60) 
inches and a pressure per linear inch of tread of at least 310 pounds, 
along the large roll, until it is compacted. All soft spots which 
are developed should be refilled and rerolled. The surface thus 
prepared must conform closely to the prescribed cross-section of 
the street. 

Upon this foundation, broken stone, preferably the run of 
crusher, gravel or clean sand, will be laid to the depth of three 
(3) inches and thoroughly consolidated by rolling, to be followed 
by the hydraulic concrete, the latter in this way not being brought 
in contact with the soil and drainage being provided by the broken 
stone. 

This form of construction is most necessary in very cold climates 
and especially on clay soils where a thaw is apt to occur from 
the action of frost, and where cracks have been observed to open 
in the ground and extend through the concrete and the asphalt 
surface. 

1 See footnote on page 447. 



SPECIFICATIONS. 449 

As an additional precaution under such conditions the follow- 
ing provisions are made as to setting the curb: 

Curbing. — Curb of the character described shall be set in con- 
crete in a trench. .. .inches deep, the bottom of which is filled 
with broken stone to a depth of ... .inches, connected with the 
broken stone cross trenches of the base, upon which shall rest 
the concrete foundation for the curbstone, not less than six (6) 
inches thick and seventeen (17) inches wide, made of the mate- 
rials in the proportions previously described for the concrete base, 
except that the stone shall not exceed one and one-quarter (1|) 
inches in maximum dimension. The curb shall be imbedded 
immediately in the centre of this concrete and backed up with 
additional concrete for a width of six (6) inches, extending from 
the concrete base to within four (4) inches of the top of the curb. 
The broken stone underlying the concrete shall be graded to catch- 
basins for the removal of ground-water. 

Sandy Soils. — On sandy soils at the seashore, where it is diffi- 
cult to compact the sand under the roller, it may be provided 
that a course of one (1) or two (2) inches of gravel or other suit- 
able material may be spread and rolled over the sand before the 
concrete foundation is constructed 

Asphalt. — While, in the author's opinion, there is no question 
that the best asphalt surface, in the present state of the industry, can 
be constructed with Trinidad lake asphalt or gilsonite, he would not 
be understood to affirm that satisfactory work cannot be done with 
other bitumens, and for streets of light traffic the Engineer may 
exercise such choice as he may believe to be desirable from the 
point of view of competition. He should, however, bear in mind 
that the skill which the contractor may possess and his knowl- 
edge of the art of constructing an asphalt pavement is of as great 
importance as the materials in use or the price which may be bid. 
At an equal cost the pavement constructed with skill and intelli- 
gence may be worth a very much larger sum when completed 
than another surface carelessly constructed. These points should 
weigh largely in the awarding of contracts if the cost of main- 
tenance of the surface to the city after the expiration of the guar- 
antee period is to be considered. 



450 



THE MODERN ASPHALT PAVEMENT. 



Grades of Streets on which Asphalt Pavements may be Con- 
structed. — The general impression has gained ground, very natu- 
rally, that asphalt pavements are unsuited to grades of more than 
4 to 5 per cent. That this is an erroneous conclusion may be seen 
from the fact that in 1890 an asphalt surface was laid in Wash- 
ington, D. C, on Thirty-fourth Street, N. W., from M Street to 
Prospect Street, 275 feet long, the grade of which is 9.74 per cent, 
and that in Kansas City, Mo., the following streets have been con- 
structed with the grades given. 1 



GRADES IN KANSAS CITY, MO., FOR ASPHALT PAVEMENTS. 



Year Laid. 


Street. 


Grade. 


1898 
1895 
1897 
1895 
1894 


Jefferson Street, 18 to 20 

11 Street, Maine to Wyandotte. . 
Troost Ave., 19 to Belt Line. . . . 

Central Street, 16 to 17 

Forest Ave., Independence to 8. 


12.5% 

7.5 

8.0 
10.0 

8.0 



All of these streets are in constant use and are satisfactory 
except on occasions where a thin coating of moisture has 
become congealed on the surface. Several of the streets in Kan- 
sas City are only paved with asphalt in the centre, the sides 
having a stone or brick surface. Nevertheless, the asphalt sur- 
face is universally used in preference to the brick or stone, and 
appears to be no more slippery even under the most trying con- 
ditions. Where a film of ice causes asphalt to be slippery traffic 
is diverted to other streets with lighter grades, rather than to the 
brick or stone. As a matter of fact the limiting conditions in 
determining the extent to which the steepness of a grade will 
prevent the use of an asphalt surface mixture will depend entirely 
upon the climate and the nature of the traffic which uses the street. 
Eight per cent is not an excessive grade under ordinary eastern 
conditions, while in a climate like Seattle, Wash., a 10 per cent 
or 12 per cent grade is quite possible. 

1 Tillson cites a grade of 17 per cent on a portion of Bates Street, in 
Pittsburg, Pa., and 12| per cent in Scranton, while Baker mentions one of 
16 per cent in San Francisco, Cal. 



SPECIFICATIONS. 



451 



Crown or Camber. — That an asphalt pavement should show 
in transverse section a proper profile for the surface is as important 
as that the grade should be sufficient to provide for proper drain- 
age. There is little agreement among engineers in regard to 
what this proper form should be, but it is quite certain that the 
tendency in America is to make all the asphalt pavements much 
too flat. Theoretically, no doubt, an asphalt pavement should 
demand but a low crown or camber. In practice, however, the 
pavement will prove much more satisfactory and pleasing to 
the eye if this is maintained at a comparatively high figure, since 
in wet weather the slight depressions which it is impossible to 
avoid in laying such a surface, or which are formed by unequal 
compression and traffic, will not then be revealed as small pools 
of water. This is especially the case if the profile of the surface 
shows a plane surface from the gutter to the crown instead of a 
curve. 

It is generally assumed that for a roadway 30 feet wide a 
crown of 4 inches should be adopted, with a curve towards the 
gutter having a somewhat greater fall near the latter and decreas- 
ing towards the crown. The objection to this profile is that the 
street is too flat on the crown, with the result that depressions form 
there which retain water. It is, therefore, much better to keep 
the crown raised sufficiently to avoid this. On the other hand, 
with a nearly flat crown, the centre of the street which is used 
principally for traffic is of a more acceptable form. Mr. G. W. 
Tillson 1 gives the following table showing the necessary crown 
for streets of a width from 24 to 60 feet. 



Width of roadway 

Crown 

Fall towards gutter in cen- 
tral J of roadway 

Rate per 100 ; 

Fall towards gutter in sec- 
ond £ of roadway 

Rate per 100 

Fall to gutter in £ of road- 
way adjacent to curb. . 

Rate per 100 



24 ft. 


30 ft. 


30 ft. 


36 ft. 


48 ft. 


3 ins. 


4 ins. 


6 ins. 


5 ins. 


6 ins. 


$ in. 
83- ins. 


4 in. 

9 ins. 


1 in. 
\Z\ ins. 


f in. 
9i ins. 


t in. 
8^ ins. 


1 in. 
2' 1" 


\\ ins. 
2' 3" 


2 ins. 
3 / 4 // 


If ins. 
2" 4" 


2 ins. 
2' 1" 


If ins. 
3' 6" 


2f ins. 
3' 8" 


Z\ ins. 
5' 6" 


21; ins. 
3' 3" 


Z\ ins. 
3' 6" 



60 ft. 
8 ins. 

t in. 
8f ins. 

2f ins. 
2' 3" 

41 ins. 
3' 9" 



Street Pavements and Paving Materials, 202. 



452 



THE MODERN ASPHALT PAVEMENT. 



The author would regard an 8-inch crown as none too high 
for a 60-foot roadway, while on many flat streets a 6-inch crown 
is not too high for a 30-foot roadway. Of course the steeper the 
grade of the street the smaller the height of crown which is 
necessary, and this fact does not seem to have been taken into 
consideration in the table which Tillson offers. 

In Paris, France, the crown for asphalt streets is determined 
by the formula, Fig. 26. 

Provision is made for a drop of 10 per cent from the point A 
towards the curb for a space of 50 cm. (19.7 inches). This latter 
provision seems to the author to be an excellent one and, from 
his experience in Paris, the form of street profile to be a very suc- 
cessful one. 

Baker x gives a resume of the specifications of various cities 





Fig. 26. 



NL 2 
^=0.012^, 

AB= 0.05 meters. 

for crowns of asphalt pavements to which the reader may refer. 
The provisions of the City of Omaha are also very excellent. 



1 Roads and Pavements, 348. 



SPECIFICATIONS. 



453 









TABLE 


OF 


STANDARD 


CROWNS 












(City Engineer's Office, Omaha, Neb., 1902.) 










Crowns for American Sheet Asphalt Pavement in 


Feet. 






Distance 


Grade of Street. 










Between 












Curbs. 














"a3 
> 


1% 


2% 


3% 


4% 


5% 


6% 


7% 


8% 


9% 


10% 


n% 


12% 


20 feet. . . . 


.40 


.38 


.37 


.35 


.34 


.32 


.30 


.29 


.27 


.26 


.24 


.22 


.21 


25 « 4 




.50 


.48 


.46 


.44 


.42 


.40 


.38 


.36 


.34 


.32 


.30 


.28 


.26 


30 ' 


• . . . 


.60 


.58 


.55 


.53 


.50 


.48 


.46 


.43 


.41 


.38 


.36 


.34 


.31 


35 ' 


. . . . 


.70 


.67 


.64 


.62 


.59 


.56 


.53 


.50 


.48 


.45 


.42 


.39 


.36 


40 ' 




.80 


.77 


.74 


.70 


.67 


.64 


.61 


.58 


.54 


.51 


.48 


.45 


.42 


45 ' 




.90 


.86 


.83 


.79 


.76 


.72 


.68 


.65 


.61 


.58 


.54 


.50 


.47 


50 " 




1.00 


.96 


.92 


.88 


.84 


.80 


.76 


.72 


.68 


.64 


.60 


.56 


.52 


55 ' 




1.10 


1.06 


1.01 


.97 


.92 


.88 


.84 


.79 


.75 


.70 


.66 


.62 


.57 


60 * 




1.20 


1.15 


1.10 


1.06 


1.01 


.96 


.91 


.86 


.82 


.77 


.72 


.67 


.62 


65 ' 


• . 


1.30 


1.25 


1.20 


1.14 


1.09 


1.04 


.99 


.94 


.88 


.83 


.78 


.73 


.68 


70 ' 


• . . . 


1.40 


1.34 


1.29 


1.23 


1.18 


1.12 


1.06 


1.01 


.95 


.90 


.84 


.78 


.73 


75 ' 




1.50 


1.44 


1.38 


1.32 


1.26 


1.20 


1.14 


1.08 


1.02 


.96 


.90 


.84 


.78 


80 " .... 


1.60 


1.54 


1.47 


1.41 


1.34 


1.28 


1.22 


1.15 


1.09 


1.02 


.96 


.90 


.83 



Note. — The formula used for the construction of the table is as follows: 



C = 



17(100 -4/) 
5000 



C = crown of pavement in feet ; 
W= distance between curbs in feet; 
/= number of feet fall per 100 feet of street. 
Note. — Where the crown is less than 0.5 foot make the gutter 0.5 foot, 
and where it is 0.7 foot make the gutter 0.7 foot, and for intermediate crowns 
make the gutter equal the crowns. — Andrew Rosewater, M. Am. Soc. C. E., 
City Engineer. 



None of these methods of arriving at a proper figure for crown 
is applicable if opposite sides of the street are not of the same 
elevation. 

The subject of the form to be given to streets is discussed at 
much length and with reference to various cases in ' ' Traite 
Pratique des Travaux enAsphalte," Letouze etLoyeau, Paris, 1897, 
and reference must be made to this work for more detailed formula 
and special applications. 

Gutters. — In many cities where concrete curb and gutter are 
not in use, there has been a tendency to use either stone or brick 



454 THE MODERN ASPHALT PAVEMENT. 

as a substitute for an asphalt surface in gutters of asphalt streets. 
From what has been shown in the previous pages it is evident 
that where the asphalt-surface mixture is made on the lines laid 
down by the author, and where the form of construction employed 
in the street is such as to provide satisfactory drainage, there is no 
reason why the asphalt surface should not be carried from curb to 
curb, nor is there any necessity for painting such a surface with 
asphalt or bitumen, if the mixture of which it is composed is 
constructed on modern lines. In the early days of the industry 
this painting became the custom, owing to the fact that the 
mixtures were made with sand so badly graded and so porous 
that they could not resist water action. 



CHAPTER XXIII. 

THE MERITS OF THE MODERN SHEET-ASPHALT PAVEMENT. 

Whether a sheet-asphalt pavement possesses any lasting degree 
of merit will depend entirely upon the manner in which it is con- 
structed from the base up, including proper drainage and the charac- 
ter of the asphalt mixture which forms the surface. It has already 
been made evident that the greatest care is necessary in all these 
respects. It will be only worth while, therefore, to consider 
what the merits are of a sheet-asphalt pavement of standard 
construction. Such a pavement is desirable for the following 
reasons : 

1. It does not disintegrate under impact or attrition, and con- 
sequently produces neither mud nor dust. 

2. It can be kept perfectly clean if the proper efforts are made 
to do so. 

3. It has an impervious surface and does not absorb filthy 
liquids, as is the case with wood blocks. 

4. It affords the best foothold for horses except under occa- 
sional conditions. 

5. Traction on such a surface can be carried on with a smaller 
expenditure of force than on any other form of pavement. 

6. Its wearing properties compare more than favorably with 
granite and exceed that of any other form of pavement under 
heavy traffic. 

7. Deterioration in a standard asphalt pavement is of a kind 
that can be readily and economically met owing to the simplicity 
of making repairs, something that cannot be done satisfactorily 
with any other form of pavement. 

455 



456 THE MODERN ASPHALT PAVEMENT. 

8. Cuts in the pavement for underground work can be replaced 
in a manner which makes the repairs undistinguishable from 
the original surface, whereas they are quite evident in the case 
of other pavements. 

9. It increases the actual and rental value of all real estate 
abutting on streets where it is laid to a larger extent than any 
other form of pavement. 

10. The wear and tear upon horses and carriages is largely 
reduced by asphalt pavements, and it has been estimated for 
Philadelphia x that the repairs to vehicles in that city due to 
rough pavements existing there in 1885, which could be saved 
by sheet-asphalt pavements, would amount to $1,000,000 annually. 
The universal testimony of fire-department chiefs is that there is 
far less wear and tear to the running gear of the engines, hose 
carriages and trucks on asphalt pavements than on stone blocks, 
and consequently less liability to break down or to have acci- 
dents, while much better time is made in going to fires. 

That asphalt pavement will sustain the heaviest traffic that 
is carried by any street in the world can be seen from the follow- 
ing determination of the number of vehicles and the tonnage on 
Fifth Avenue and some other streets in New York City during the 
months of November and December, 1904. See table on page 457. 

The heaviest traffic in London, as determined in 1879, was 
422 tons per foot of width per day. The traffic on Fifth Avenue, 
which has been an extremely successful asphalt pavement, is, 
therefore, equal to, if not greater than, that sustained by the pave- 
ment on many of the most heavily travelled streets of Europe. 

The defects which have generally been assigned to an asphalt 
pavement are its comparatively great first cost and cost of main- 
tenance. Its first cost may be larger than that of some other 
inferior forms of pavement, but considering the length of time 
that an asphalt surface will wear, if of standard construction, this 
cost is smaller per annum and per ton of traffic carried than 
that of any other form. The cost of maintenance has no doubt 
been large for many pavements constructed in the past and will 
be large for many constructed in the future which are not of stand- 

1 The Philadelphia North American, Oct. 12, 1885. 



MERITS OF THE MODERN SHEET-ASPHALT PAVEMENT. 457 

ard composition. With the best form of construction the cost 
per yard will not be excessive and the public will have the advan- 
tage, if the city maintains its streets, which unfortunately is not 
always the case, of having a perfect pavement at all periods of 
its existence, instead of one which becomes worse and worse with 
each year of its age. 

Another defect has been said to be the fact that it is unsuited 
for steep grades. From the figures given on pages 450 and 451 
it is evident that this is not so. 

There can be no question that a standard sheet-asphalt pave- 
ment possesses more merits than any other, and fewer defects. 
It is undoubtedly the pavement of the present and of the future. 

TRAFFIC RECORD TAKEN ON STREETS PAVED WITH ASPHALT 
IN NEW YORK, N. Y., NOVEMBER AND DECEMBER, 1904. 



Fourth Street, from Wooster 

to West Broadway 

Eighth Avenue, from 35th 

to 36th Streets 

Thirty-fourth Street, from 

Broadway to Seventh Av . 
First Avenue, from 26th to 

27th Streets 

Fifth Avenue, from 33d to 

34th Streets 

Broadway, from 18th to 19th 

Streets 



Tonnage 

per 
11 Hours. 



9254.22 
13024.52 

2176.60 
19253.76 
19274.47 

7491.70 



Average 
Tonnage 
per Linear 

Foot of 
Width per 
11 Hours. 



289 . 18 

296.02 

89.22 

435.58 

481.85 
299 . 63 



Average 
Tonnage 
per Hour. 



841.35 
1184.05 

197.86 
1750.34 
1752.20 

681.06 



Average 
Number of 

Vehicles 

per 
11 Hours. 



3394 
5720 
1072 
6034 
11787 
3817 



Average 
Tonnage 

per 
Vehicle. 



2.73 
2.28 
2.03 
3.18 
1.64 
1.97 



The Cost of Asphalt Pavements. — No general statement can 
be made in regard to the cost of an asphalt pavement, as it is a 
function of too many variables; these variables can, however, be 
considered individually. They are: 

1. Freight rates for the transportation of the plant and mate- 
rials of construction to the locality where the pavement is to 
be laid. 

2. Local cost of materials of construction, such as sand, cement, 
gravel, broken stone, and filler. 



458 THE MODERN ASPHALT PAVEMENT. 

3. The cost of local labor. 

4. The form of construction which is specified. 

5. The character of the traffic which the street is to carry, 
its grade, and the character of the pavement on adjoining streets. 

6. The period of guarantee demanded. 

7. The terms of payment. 

With so many changeable conditions it would, of course, be 
impossible to give any general data as to the cost of an asphalt 
pavement. It may vary from $4 or $5 per yard on a street of 
extreme traffic in a large city which is guaranteed for 15 years, 
and $1.25 per yard on old brick pavement for the base where 
the traffic is very light, as in a residence street or where no guar- 
antee is demanded, as is the case in the State of California. 

Cost of Maintenance. — The cost of maintenance is quite as 
uncertain an element as the cost of construction; and even more 
so, since it will depend not only on the character of the original 
work but upon the amount of attention which is given by the 
company constructing the pavement, or by the authorities after 
the former's guarantee has expired, to keeping the surface in first- 
class condition. If it is neglected the cost of maintenance may 
become large, whereas if carefully kept up this may well be small. 

The character of the base which supports the pavement will 
have more to do with the cost of its maintenance, if the surface 
is a standard one, than any other controlling condition. In the 
observation of the writer at least 90 per cent of all maintenance 
work on asphalt pavements with well-constructed surfaces is due 
to weakness and deficiency in the base. 

It is of interest in this connection, however, to note the data 
contained in a paper by Capt. H. C. Newxomer, Corps of Engineers, 
United States Army, in regard to the cost of maintenance of the 
asphalt pavement in Washington, D. C, especially as the sur- 
face mixtures laid in that city have been, unfortunately, not of 
standard quality, owing to deficiencies in the character of the 
local sand supply. Capt. Newcomer has found 1 that " the aver- 
age cost per square yard per annum for the second five-year period 
of the life of the pavements considered was 1.65 cents; for the 

1 Engineering News, 1904, Feb. 18, 51, 165. 



MERITS OF THE MODERN SHEET-ASPHALT PAVEMENT. 459 

third five-year period, 3.37 cents; for the fourth five-year period, 
3.78 cents, and for the fifth five-year period, 2.56 cents. The 
average cost for all ages tabulated was 2.8 cents." 

It is worthy of note in this connection that of the 2,425,732 
square yards of bituminous pavements of all kinds, including coal- 
tar, in the preceding estimate, many of which were very inferior, 
not less than 2,161,181 square yards were constructed of Trinidad 
asphalt. 



CHAPTER XXIV. 
ACTION OF WATER ON ASPHALT PAVEMENTS. 

The action of water on asphalt and on asphalt pavements 
has been a prominent topic of discussion from the early days of 
the industry, and the subject, for many reasons, remains one of 
peculiar interest to-day, since many mistaken ideas in regard 
to it are still in vogue. 

Asphalt surface mixtures, the mineral aggregate of which is 
not properly graded and balanced and which, in consequence, 
lack density and an impervious surface, are attacked by water 
when subjected to its continued action, from lack of proper drain- 
age or other reasons, without regard to the nature of the asphalt 
of which the mixture is made, although under these conditions 
one asphalt may be attacked more than another. With the stand- 
ard surface mixture constructed on the ideas laid down by the 
author in the previous pages surface mixtures may be constructed 
of any asphalt which are equally resistant to water action, but 
all of which are attacked more or less by the water unless allowed 
to dry out at intervals. In a properly constructed pavement no 
important deterioration from water action should ensue within 
the life of the pavement and, as a matter of fact, in the author's 
experience, the deterioration in the asphalt surfaces laid under 
his supervision has in the last ten years become an item which 
is hardly worth consideration, where the form of construction 
has provided satisfactory drainage. 

As it must be admitted that asphalts are attacked by water 
to different degrees when the mixtures are not dense, and espe- 
cially in laboratory tests, it is of interest to examine into the rea- 

460 



ACTION OF WATER ON ASPHALT PAVEMENTS. 461 

son for this, in order that we may be able to compare practical 
results with those obtained by experiment and determine the 
means for preventing such action on pavements actually in use. 

Numerous observers have detected and noted the fact that 
there is a difference in the degree to which water acts upon vari- 
ous asphalts and fluxes. Messrs. Whipple and Jackson have made 
an elaborate investigation of the subject, the results of which 
were presented in a paper read before the Brooklyn Engineers' 
Club in March, 1900, which was published in the Engineering 
News for March 22, 1900. These results, although of little inter- 
est as showing the effect of water on a well-constructed asphalt 
paving mixture, since the pure bitumens were themselves exposed 
by these investigators directly to the continued action of water 
in order to determine their relative value for the construction of 
concrete lining for reservoirs and not for pavements, are of inter- 
est as showing that experiments conducted under conditions 
employed by these investigators may lead to conclusions which 
are utterly erroneous as applied to the paving industry, except 
when the asphalts in question are used in an unskillful way. 

Actual Results on the Streets. — It is of interest to consider 
what the practical experience has been on the street during 
the last fifteen years as regards the action of water on asphalt 
surface mixtures. In the early days of the industry, as has already 
appeared, the asphalt surface mixtures were very open. At the 
time that the author was connected with the Engineer Department 
of the District of Columbia the Trinidad asphalt surface mixtures 
were constructed with coarse sand and very little filler. The 
gutters of streets which were paved with mixtures of this descrip- 
tion were much given to deterioration from the action of water, 
and the same conditions were met in other cities, so that at that 
time every one believed that it would be impossible to construct 
a Trinidad surface mixture which would not be attacked by water. 
This idea has persisted in the minds of many who have not followed 
the industry carefully down to the present day, and it was only 
dissipated in the author's mind by an experience extending from 
1894 to 1896 during an attempt to introduce the American form 
of asphalt pavement in London, England. In 1894 a Trinidad 



4G2 THE MODERN ASPHALT PAVEMENT 

asphalt surface was constructed on Pelham Street, Kensington, 
and on King's Highway, Chelsea, in London, using Trinidad asphalt 
in much the same way that he had employed it in previous years 
in Washington, D. C, the modern methods of constructing a 
mixture to withstand heavy traffic and wet climate not having been 
developed at that time. The results were that the pavements 
were not an entire success and scaled. It was suggested that 
this was due to the fact that the asphalt in use was Trinidad and 
that this was constantly attacked by the continuous fogs of London. 
The pavements were, therefore, replaced in the following year 
with a mixture made with Bermudez asphalt. These surfaces 
went to pieces much more rapidly than the previous Trinidad 
surfaces. By this time the principles which have been elucidated 
in the preceding pages had been largely worked out. In the third 
year Trinidad asphalt surfaces were laid in London on these lines 
which not only were not attacked by the continued wet weather 
and fogs of that climate, but which have remained there to the 
present time, having shown no deterioration due to water action. 
If the Bermudez surfaces had been constructed with the same 
regard to the mineral aggregate and to the character of the asphalt 
cement prepared from it they would undoubtedly have shown 
an equal freedom from the action of water, but it is not probable 
that they would have shown an equal resistance to the deteriorating 
influence of the heavy traffic on the streets on which the pavements 
were laid. Practical experience rather than theory, therefore, leads 
the author to conclude that an asphalt which may not appear to be 
as satisfactory in laboratory tests may prove more so in actual 
construction. 

That asphalts which are not attacked by water in the laboratory 
may be seriously affected by it in asphalt surface mixture has 
frequently been revealed, but never in a more striking way than 
in Reading, Pa., where house drainage is conducted along the 
gutters of the Bermudez asphalt pavements of that town, in con- 
sequence of which they have entirely disintegrated, as shown in 
the accompanying illustration, Fig. 27. 

It appears then that it is the manner in which the asphalt is 
used and the practical results obtained with it rather than its 




>> 

rO 



4G4 



THE MODERN ASPHALT PAVEMENT. 



properties as revealed by laboratory tests which should control 
cur judgment in forming an opinion of its behavior towards water 
in an asphalt-surface mixture on the street. 1 

As a practical example of the difference between surface mix- 
tures actually in use and made with different asphalts in their rela- 
tion to water absorption in the laboratory, the results of an examina- 
tion of the Trinidad and Bermudez surface mixtures which vere 
being laid in the city of New York in the year 1904 may bt of 
interest. These mixtures consisted of the following material!* >j> 
the proportions given and had the following composition" 



Proportions. 


Trinidad. 


Bermudez. 


Sand (1 Cow Bay and 1 Crossman) 
FLler (P. C. dust) 


74.7% 
9.6 
15.7 


73.7% 

14.8 

11.5 


Asphalt cement 


Analyses. 
Bitumen 


100.0 

11.0% 

16.0 

11.0 

11.0 

24.0 

13.0 

7.0 

4.0 

3.0 


100.0 

H.2% l 

17.8 

12.0 

10.0 

27.0 

12.0 

5.0 

3.0 

2.0 


Passing 200-mesh sieve 


< ' 100- " ' ' 


" 80- ' ' " 


50- " " 


*' 40- " " 


" 30- " " 


" 20- " " 


10- " " 




100.0 


100.0 



Of the above mixtures cylinders 1 inch in height were made 
having the greatest density possible, by compressing them under 
impact in a diamond mortar of a diameter of 1.25 inches. The 
cylinders of mixtures had the following densities and weight: 



1 This subject has been discussed at length in the Engineering News, 
1904, June 2, 51, 520. 



ACTION OF WATER ON ASPHALT PAVEMENTS. 



435 



Cylinder 
Number. 


Trinidad. 


Bermudez. 


Density. 


Weight 
(Grams). 


Density. 


Weisjht 
(Grams). 


1 

2 

3 

4 

5 

6 

Average. 


2.247 
2.200 
2.204 
2.217 
2.214 
2.223 

2.217 


47.522 
47.227 
46.963 
46.885 
48.536 
49 . 548 

47.780 


2.262 
2.225 
2.232 
2.277 
2.222 
2.260 

2.246 


46.728 
47.410 
47.551 
49.631 
49.410 
52.257 

48.831 



These cylinders were exposed to the action of running water 
for a length of time. The gain in weight of the cylinders at various 
intervals is shown in the following table in fractions of a pound per 
square yard : 

ABSORPTION OF WATER. POUNDS PER SQUARE YARD. 







Trinidad. 






Bermudez. 




Cylinder 
Number. 


































l 


4 


2 


3 


1 


4 


2 


3 




Week 


Weeks. 


Months. 


Months. 


Week. 


Weeks. 


Months. 


Months 


1 


0849 


.1111 


.1262 


.1291 


.0961 


.1020 


.1183 


.1174 


2..... . 


0789 


.1009 


.1190 


.1194 


.1485 


.1428 


.1640 


.1694 


3 


.0763 


.0991 


.1149 


.1171 


.0868 


.0914 


.1134 


.1103 


4 


.0869 


.1069 


.1199 


.1240 


.0694 


.0883 


.1077 


.1089 


5 


.0839 


.1066 


.1237 


.1254 


.0909 


.0966 


.1198 


.1194 


6. 


.0706 


.0943 


.1137 


.0914 


.0526 


.0566 


.0746 


.0729 


Average. 


.0803 


.1031 


.1196 


.1177 


.0940 


.0963 


.1163 


.1164 



After an exposure of three months none of the cylinders 
showed any signs of softening. Those containing Bermudez 
asphalt could, however, be distinguished from those made with 
Trinidad asphalt by slight excrescences the size of pin-heads, 
which had appeared upon the surface. Fig. 28. It must be 
remembered, too, that the cylinders were not prepared from mix- 
tures made in the laboratory, but were made from material which 
was actually being used on the street. 



466 



THE MODERN ASPHALT PAVEMENT. 



When pieces of glass were coated with Trinidad and Bermudez 
asphalt cement and with one made from a California residual pitch 
and immersed in running water for a week they were all more or 
less attacked thereby, as can be seen from the accompanying 
illustration, Fig. 29. From the preceding results it is apparent 




Trinidad Lake Asphalt, Bermudez Asphalt. 

Surface Mixture. 
In running water five months. 
Fig. 28. 

at once that although all asphalts under certain circumstances 
are attacked by water, Trinidad asphalt when properly used in an 
asphalt surface mixture is the equal of any other in resisting 
power, and this fact being proved to a contractor's satisfaction, he 












1 F 




V 


■■if 




California Oil 
Asphalt Cement. 



Bermudez 

Asphalt Cement. 

In running water one week. 

Fig. 2d. 



Trinidad Lake 
Asphalt Cement. 



ACTION OF WATER ON ASPHALT PAVEMENTS. 467 

prefers to employ it for the many reasons which have been given 
in another place, namely, because no other material offers such a 
uniform supply as that taken from the Trinidad pitch lake, every 
cargo being handled in the same manner as those preceding it, 
because the bitumen which it contains is free from hydrocarbons, 
which are volatile at the temperature at which it is necessary to 
maintain a surface mixture, m consequence of which asphalt cement 
made with it from proper flux is peculiarly non-volatile and non- 
changeable at this temperature, and because it can be maintained 
for a considerable length of time at high temperatures without 
hardening excessively, even when tossed about loosely with exces- 
sively hot sand in any process of turning out the surface mixture. 

Cause of the Action of Water on Asphalt Under Certain Cir- 
cumstances. — All bitumens, as has been seen, are more or less 
acted upon by water under certain conditions. It is a matter of 
great interest to determine what conditions are most favorable 
for the destructive action of water, how far this action is inherent 
in certain properties of the bitumen, and how far to the presence 
of gases or salts soluble in water, or of the latter mixed with 
the asphalt. 

There has been a great cry that the soluble salts in Trinidad 
asphalt were the cause of the deterioration of this material in the 
presence of water. The idea unfortunately originated with the 
author many years ago on insufficient evidence. It was soon shown 
that the addition of 5 per cent of common salt to a Trinidad asphalt 
surface mixture or immersion of the latter in salt water com- 
pletely prevented any disintegration, even of the old-time open 
surface mixture. This, of course, quite does away with the idea 
that the presence of soluble salts in Trinidad asphalt has any- 
thing to do with its disintegration when exposed in the refined 
condition to the continued action of water. As a matter of fact, 
the bitumen of Trinidad asphalt is not in itself attacked by sea- 
water under the conditions imposed by Messrs. Whipple and 
Jackson. 

When the material which has become disintegrated and brown 
under these tests is remelted the original bitumen is recovered in 



468 



THE MODERN ASPHALT PAVEMENT. 



an unchanged condition, both as to consistency and softening point. 
The action of the water seems, therefore, to be in this case caused 
by its absorption by some of the organic matter or non-bituminous 
matter which the asphalt contains. If the vegetable matter is so 
sealed up in the asphalt or in the surface mixture as to prevent 
diffusion no disintegration occurs. As a preventive against the 
slightest diffusion the presence of a material, such as Portland 
cement, which will combine with the water is desirable. 1 

That asphalt surfaces can be constructed from any asphalt 
so that they will not be attacked by water has been conclusively 
proved within the last few years. In the same way it has been 
equally conclusively proved that all asphalts, under certain con- 
ditions, are more or less attacked by water. 

That a distinct advance has been made along this line can be 
seen by comparing the amount of water absorbed by the surfaces 
of 1894 as compared with those of ten years later, as shown in the 
following table: 

ABSORPTION OF WATER BY CYLINDERS OF ASPHALT SUR- 
FACE. IN POUNDS PER SQUARE YARD. 





Washington, 1893. 


Standard Mixture, 1904. 


Trinidad. 


Bermudez. 


Trinidad. 


Bermudez. 


7 days. . 
14 " .. 
28 " .. 


.314 
.434 
.502 


.063 

.194 
.306 


.080 
.093 
.107 


.094 
.093 
.104 



The conditions to which asphalt surface mixtures are sub' 
jected in the street and in the laboratory bear no relation to one 
another. In the ordinary laboratory tests surface mixtures are 
submitted to the continued action of water, except when bur* 
nished from time to time with a burnishing-tool for experimental 
purposes, and receive no compaction as does the street surface 
from the traffic which it receives. In the street an asphalt sup- 

1 See page 27: P. C. as a Filler. 






ACTION OF WATER ON ASPHALT PAVEMENTS. 469 

face is never subjected, at least in well constructed pavements, 
to the continued action of water. The conditions are, there- 
fore, in this respect very different from any which are found in 
laboratory experiments. The conclusion must, therefore, be 
drawn that we must be guided in forming an opinion in regard 
to the availability of any material by the results obtained in prac- 
tice and not by theoretical deductions from laboratory experi- 
ments. The asphalt surface laid on Fifth Avenue, New York, 
a thoroughly well-constructed surface, if the presence of an open 
binder is barred, has been practically unacted upon by water, 
although made of Trinidad asphalt, in the ten years of its exist- 
ence, since no repairs of any amount have been made to the pave- 
ment due to deterioration of the mixture. No doubt a very 
small amount of deterioration may be detected in the gutters 
along the curb, but this would have been the same in the case of 
other asphalts as in the Trinidad mixture and does not reach an 
extent to demand consideration. 

In this connection it is of interest to call attention to the fact 
that a process has been patented for washing crude Trinidad 
asphalt for the removal of soluble salts before it is refined, and 
that it is true that material thus treated withstands laboratory 
tests to a somewhat better degree than the untreated material 
when exposed to the action of water in the refined condition, but 
the behavior of the surface mixture is not improved by it to any 
appreciable extent, and the process must, therefore, be regarded 
as involving an additional expense with no compensating return. 

In conclusion the author may state with the utmost conviction 
that no Trinidad asphalt pavements which have been laid under 
his direction in the last ten years have suffered from the attack 
of water when a proper form of construction has been employed. 
All attempts which have been and are now being made to prove 
the contrary are based purely upon personal and political attempts 
to disparage the nature of the material. 

SUMMARY. 

An endeavor is made in the preceding chapter to show that 
the conclusions derived from laboratory experiments and from 



470 THE MODERN ASPHALT PAVEMENT. 

the results of poor workmanship, as regards the action of water 
on asphalt surfaces, are not practical, but merely theoretical. It 
is shown that with requisite skill, surface mixture can be made 
from those asphalts which are themselves attacked by water in 
the refined state in the laboratory which will not be at all 
attacked by water either in the laboratory or on the street. 
Statements to the contrary generally originate in a desire to damage 
the reputation of a material for reasons arising in business rivalry. 



PART VIII. 

CAUSES OF THE DEFECTS IN AND THE DETERIO- 
RATION OF ASPHALT SURFACES. 



CHAPTER XXV. 
DEFECTS IN AND DETERIORATION OF ASPHALT PAVEMENTS. 

Asphalt surfaces, like all pavements, necessarily deteriorate 
with age even when they are originally of the most acceptable 
form of construction. When they are not well constructed they 
deteriorate very rapidly. 

Defects in asphalt surfaces are more apparent than in any 
other form of pavement, since it is a continuous, smooth surface 
without joints. The eye, as well as the effect of any irregularity 
upon the vehicle passing over it, reveals them at once, where the 
difference between a perfect and worn stone or brick surface is 
not as noticeable. 

The proper method of construction of an asphalt pavement 
and the characteristics of a desirable asphalt surface mixture 
have already been elaborated. At this point it seems appropriate 
to sum up the causes of the deterioration in such surfaces which 
are due to defects in construction or environment and to follow 
this with an examination of the causes of legitimate wear. 

Deterioration of or defects in asphalt pavements are attributed 

to three principal causes and many minor ones: 

471 



472 THE MODERN ASPHALT PAVEMENT. 

1. Defects in construction due to 

A. Improper specifications or form of construction'. 

B. Lack of lateral support. 

C. Inferiority of sand, in the character of the filler or lack 

of a sufficient amount of it. 

D. Inferiority in the asphalt or lack of intelligence in its use. 

E. Careless workmanship and ignorance. 

2. Unfavorable environment. 

A. Climate. 

B. Lack of cleanliness and general neglect. 

C. Action of water, of illuminating-gas, or of gas and water 

combined. 

D. Flushing with water under pressure. 

E. Constant opening of the surface for underground work. 

3. Age. 

A. Natural wear. 

B. Neglect of maintenance. 

Improper Specifications. — It often happens that from motives 
of economy specifications provide for a form of construction of 
asphalt pavements which is deficient in one or more respects from 
what is necessary to enable them to meet the conditions to which 
they are to be exposed. 

Particular attention has already been drawn to faulty pro- 
visions for a suitable foundation and for proper drainage. It is hardly 
necessary to recur again to this matter here except to emphasize 
the fact that without a rigid foundation and proper protection of the 
surface mixture from water reaching it from the bottom, or standing 
on or flowing constantly over the top, an asphalt pavement in 
every other way of the highest type of construction cannot have 
a long life, at least without extensive maintenance. 

Specifications are also at fault in regard to the depth of the 
binder course required. An inch of binder made of inch stone 
cannot, in the writer's opinion, form a sufficient bond to keep it 
from going to pieces under constant traffic, especially if it is sup- 
ported by only a weak base. It is probable that on the heaviest 
travelled streets in our large cities an open binder course is an 
unsatisfactory form of construction. In summer when the surface 
is soft the binder is crushed under the weight of trucks with too 



DEFECTS AND DETERIORATION. 473 

narrow tires, carrying loads of as much as seven tons, particularly 
when the binder stone is not hard. The binder in such cases should 
be replaced by a denser mixture, one in which the voids in the 
stone are filled by a bituminous mortar, in fact, the regular asphaltic 
surface mixture. Such an asphaltic concrete supports the surface, 
most satisfactorily distributes the load over the base, and is of 
great advantage when placed over a base subject to vibration, 
such as stone blocks which have been reset, or laterally against a 
vibrating rail. Specifications for such a course have already 
been given. 

The thickness of surface specified is less often at fault. If 
properly supported, an inch and a half of surface made of desirable 
constituents has satisfactorily carried heavy traffic. A greater 
thickness may often be preferable for business streets, but the 
greater the thickness the greater the difficulty in raking out the 
hot mixture evenly and obtaining uniform compaction and the 
greater its liability to displacement with the formation of waves or 
inequalities in the surface. 

A very frequent fault in specifications for asphalt pavements 
is that it is provided that the street should be constructed without 
sufficient crown. The only objection that can be raised against a 
high crown is that the pavement is slippery on the quarters, but 
this is a very small objection compared to the fact that flat streets 
are unsightly because it is impossible to so grade them as to throw 
off all the water and because where water stands in this way it 
cannot but have an undesirable effect upon the surface. The 
height of a crown which a pavement should have has already been 
considered. 1 It may be added that defects due to lack of crown 
are more emphasized in careless work than when the pavement is 
laid with skilled labor and supervision. 

Lack of Lateral Support. — Attention has been called to the fact 
that a sufficient lateral support, free from vibration, is as essential 
as a rigid foundation. An asphaltic surface cannot be expected not 
to deteriorate against a rail which vibrates or against a header 
which is not rigid, where the asphalt joins some other form of 
roadway. 

1 See page 451. 



474 THE MODERN ASPHALT PAVEMENT. 

Proper provision for avoiding deterioration from these causes 
is rarely made and should receive more attention. Along a rail 
which shows the least tendency to vibration, paving brick in three 
or four rows, all laid as stretchers with broken joints in Portland- 
cement mortar, experience has shown is by far the most advanta- 
geous form of construction, or, if the asphalt surface must be car- 
ried to the rail, it should be supported on an asphalt concrete and 
not a binder. 

Inferiority of Available Sand. — The important role which sand 
plays in the construction of an asphalt surface and the great varia- 
tions which are met with in the character of this material have been 
made plain in preceding pages. It is evident that the sands 
available in one city may be far inferior to those found in another, 
but this demands only the more care in selecting the best and 
using them with the greatest skill. In two western cities it is only 
after seventeen years' experience and search for sand that the proper 
supply has been found. The great improvement brought about 
in the character of the surface mixtures now laid in these cities by 
the use of the sand finally selected is most evident and satisfactory. 
The result points out the great advantage derived from a thorough 
knowledge of the characteristics of various sands and by having in 
charge of securing supplies superintendents who are thoroughly 
acquainted with the subject. Where the superintendents are 
incompetent and do not pay sufficient attention to their sand, the 
surface mixtures which they produce are inferior. This is illus- 
trated by the mixtures laid by six companies in the city of New 
York in 1904, the grading of which is given on the following page 
in comparison with that produced under the author's supervision. 

It will be noted in the table that the mixture turned out 
under the author's supervision in 1904 is not up to the stand- 
ard. This is due to the fact that the available sand supply in 
that year was unsatisfactory. The other mixtures are, however, 
much more unsatisfactory, and, although they contain in ail 
cases a sufficient amount of bitumen, they are very deficient in 
sand grains passing the 100- and 80-mesh sieves and generally 
contain far too much coarse material of 10-, 20-, and 30-mesh 
size. Such mixtures, on this account, cannot result in a sur- 



DEFECTS AND DETERIORATION. 



475 



AVERAGE COMPOSITION OF MIXTURES PRODUCED IN NEW 
YORK CITY IN 1904 WITHOUT PROPER SUPERVISION OF 
THE GRADING. 



Com- 
pany 
No. 


Bitu- 
men. 


Passing Mesh. 


Re- 
tained 


















on 10. 






200 


100 


80 


50 


40 


30 


20 


10 




1 


11.0% 


9.0 


3 


7 


17 


20 


13 


12 


8 




2 


11.3 


10.7 


5 


4 


18 


11 


11 


14 


13 


2 


3 


10.4 


9.6 


5 


7 


18 


14 


13 


12 


10 


1 


4 


11.8 


12.2 


8 


6 


20 


12 


14 


11 


5 




5 


10.7 


6.3 


5 


5 


24 


18 


13 


10 


7 


1 


6 


10.8 


8.2 


4 


3 


15 


12 


15 


11 


13 


8 


7 1 .... 


10.9 


14.1 


11 


10 


28 


13 


7 


4 


2 





1 Author's mixture, 1904. 

face which will be impervious to water. It will also be noted 
that the percentage of 200-mesh material is lower than in 
that which the author supervises, although in two instances it 
is above 10 per cent, in two others over 9 per cent. It must 
be borne in mind in this connection that the sand in use contains 
a very considerable percentage of 200-mesh material, often 6 to 
9 per cent. This material is largely sand and does not act as a 
filler, so that the deficiency in the above mixtures does not seem 
as large as it really is, but they are all of them actually deficient 
in filler. In the case of companies 5 and 6 the deficiency is very 
large, and these mixtures may be pronounced very inferior on 
this account and because this deficiency is accompanied by a 
similar one in fine sand and by the presence of a very large amount 
of coarse material. 

In other cities mixtures have been laid which show even greater 
deficiencies, and illustrate very well the inferior character of the 
material which is turned out without a thorough understanding 
of the principles underlying the production of a standard surface 
mixture, and without proper laboratory control. Had the latter 
been exercised, the defects in these mixtures would have become 
apparent before the material was laid. See table on page 476. 

More gross defects in pavements are due to the improper use 
of sand than to any other causes except too hard bitumen or weak 
foundation. 



476 



THE MODERN ASPHALT PAVEMENT, 



City. 


Bit- 
umen. 


Passing Mesh. 


T3 . 
Or-i 


















^o 






200 


100 


80 


50 


40 


30 


20 


10 


M 


Buffalo, N. Y 

a it 

Chicago, 111 


9.2% 
10.6 

8.8 
11.3 

9.9 

9.9 

9.3 
10.6 

9.9 
11.1 

8.7 

9.5 

9.0 
12.7 

9.8 


4.8 
8.4 

16.2 
6.7 
4.1 
9.1 
7.7 
6.4 

12.1 
4.9 
8.3 

11.5 
5.0 
5.3 
5.2 


12 
4 

16 
4 
4 
5 
3 
6 

18 

10 
3 
4 

11 
8 

10 


19 
8 

30 
6 

27 

12 
8 
7 

30 

14 
4 
5 

12 
5 

14 


53 
31 

22 
45 
42 
44 
45 
35 
28 
33 
32 
32 
27 
53 
35 


2 

5 

2 

15 

5 

10 

11 

15 

2 

10 

26 

23 

15 

8 

14 




3 

2 

9 

4 

5 

6 

9 



11 

12 

11 

12 

4 

6 



5 
1 
1 
2 
3 
5 
5 

2 
4 
3 
5 
2 
4 



9 
2 
2 
1 
2 
5 
6 

2 
2 
1 
4 
2 
2 


16 


a it 
a 1 1 


1 


Cedar Rapids, Iowa.. . 
Erie, Pa 




Long Island City, N. Y. 

Louisville, Ky 

Newark, N. J 

New Orleans, La 

tt it a 

Omaha, Neb 


2 


Pittsburg, Pa 

Toronto, Ont 





It may happen, of course, that in some places the highest grade 
of asphalt-surface cannot be laid with the available sand supplies 
and that their lasting or wearing properties in such cities must, 
therefore, be inferior to those which can be laid in others with 
more suitable sand. 

Character of the Filler. — As has been shown x the character 
of the filler in use in asphalt-surface mixtures is very variable. If 
it is coarse and used in insufficient amount the result will be a 
decidedly inferior mixture. As an example of this, certain streets 
are known to the author, which were laid in the downtown sec- 
tion of New York in 1895, with an asphalt surface mixture con- 
taining no filler. These streets rapidly lost their shape through 
displacement of the surface or lack of stability in the mixture, 
and they have long since been resurfaced. 

It can be seen, therefore, that deterioration of asphalt pave- 
ments may at times be attributed to the lack of filler, to its poor 
character or to its unintelligent use. 

On street surfaces which are to be subjected to the heaviest 



1 See page 89. 



DEFECTS AND DETERIORATION. 477 

travel the use of Portland cement as a filler has been found to 
well repay the extra expense incurred. 

Inferiority in the Asphalt or Lack of Intelligence in its 
Use. — Defects due to the character of the asphalt in use and 
lack of intelligence in handling it are and have been the most 
frequent in pavements laid by inexperienced or unintelligent 
persons. By a proper combination of different native bitumens 
of different properties an asphalt cement can be made in which 
more or less of any available kind may form a part, but certain 
bitumens require much more skill in handling, while others will 
stand much greater abuse. Trinidad lake asphalt has been shown 
to be of the latter class, while others, either deficient in hydro- 
carbons of the malthene group, or containing light oils volatile 
at high temperatures or unsaturated hydrocarbons which readily 
become altered in their state of molecular aggregation and con- 
sequently in their consistency, are of the class which require skill 
and care in their manipulation. Others again necessitate the 
use of particular fluxing agents and result in comparative failures 
when improper ones are used. These differences have been taken 
up in the description of the properties of the several native bitu- 
mens. 

Asphalt cements made in this way with a flux which is unsuit- 
able for the purpose may thus be the cause of failure or deteriora- 
tion. Such a cement may contain an excess of paraffine scale, 
of light oils, of cracked products, or of unsaturated hydrocar- 
bons, which are rapidly converted to pitch on heating. Defects 
in asphalt surfaces have been due frequently to such reasons in 
the past. They are not as frequent to-day, but public officials 
cannot be too careful in determining the quality of the flux in 
use in preparing the asphalt cement with which a surface for 
which they are responsible is laid. Large numbers of Bermudez 
asphalt pavements laid between 1894 and 1900 were failures 
because the asphalt cement of which they were made was not 
handled with skill. 

Careless Workmanship. — Poor workmanship may be due to 
either ignorance or intention, and unfortunately it is too often 
due to both combined. The careless and irresponsible contractor 



478 THE MODERN ASPHALT PAVEMENT. 

who looks to immediate profits, who has little experience in the 
cost of maintenance of pavements, who does not set aside a cer- 
tain amount of money for this purpose or consider it in his bid 
for construction, is doing more to discredit asphalt pavements 
to-day than any inherent defects in the pavement, except per- 
haps the public officials who will not maintain their asphalt pave- 
ments after the expiration of the guarantee period. 

Aside from the defects due to the nature of the asphalt, to 
the use of improper sand and the careless regulation of the mineral 
aggregate, others are attributable to asphalt cement made, as 
has been shown, with an unsatisfactory flux, or to the fact that 
it is too hard or too soft, irregular in amount or hardened, burned 
as the saying is, by too hot sand. All lack of attention to pre- 
cautions for avoiding such defects, which are known to be fatal 
to the production of the best surface mixture, may be set down, 
largely, to carelessness as well as ignorance. 

Ignorance or lack of technical knowledge on the part of the 
contractor can be readily learned by inquiry as to whether the 
requisite technical supervision is exercised over his work by labora- 
tory methods. A high-grade surface, it has been shown, cannot 
be laid without such a supervision of all the elements entering 
into its construction. 

Intentional neglect of the proper construction from motives 
of economy can be detected by public officials if they are suffi- 
ciently acquainted with the technology of the industry. Unfor- 
tunately City Engineers are usually themselves insufficiently 
informed to do so, and it is for the purpose of instructing them 
that this book has been written. They must, as a rule, depute 
any inspection to subordinates, who are even less well informed, 
who quibble over small details and miss the important points, 
or to experts, men of no wide practical experience but rather 
theorists, with one theory one year, another the next, abandoning 
an old one for the novelty of the new, but not founding any of 
them on more than closet work and experiment, and failing to 
look back and draw conclusions of weight from practical results. 

The asphalt surfaces which are laid to-day on a rational basis, 
under the writer's supervision, are built on no theory but by deter- 



DEFECTS AND DETERIORATION. 479 

mining from a study of the composition of actual surfaces which 
have given the greatest satisfaction what a desirable form of con- 
struction is. The. manner of working out this problem has been 
elaborated in previous pages. 

Public officials are advised in determining the character of 
the work which is being done by any contractor who employs 
no scientific supervision of his process to note : 

The number of barrels of cement and the amount of sand and 
stone used in a definite area of base. 

The consistency of the asphaltic cement and its regularity, 
together with the character of the flux used in its preparation. 

The character of the sand and its capacity for carrying 
bitumen and a proper amount of filler. 

The grading of the mineral aggregate. 

The regulation of the amount of bitumen in the surface 
mixture by means of the pat paper test. 

The temperature of the materials. 

The skill in handling the materials at the plant and on the 
street. 

The Manner in Which Defects in Asphalt Surfaces Due to 
Faulty Construction are Manifested. — Defects in asphalt pave- 
ments due to the faulty methods of construction which have 
been described, are manifested in several ways. 

The surface cracks, but does not disintegrate. 

The surface cracks when the lateral support is weak and then 
goes to pieces under traffic. 

The surface disintegrates in various parts of the roadway, 
forming depressions or holes extending to the base. 

The surface, when wet, scales off in large thin patches. 

The surface is displaced upon the base becoming wavy, high 
at one spot and below grade at another. 

The surface is raised into waves by expansion of the hydraulic 
cement in the concrete base. 

Cracking in asphalt surfaces have been found to be due to 
many different causes: 

Induced by cracks in the hydraulic concrete forming the 
base. 



480 THE MODERN ASPHALT PAVEMENT. 

Produced by too hard a bitumen in the surface mixture, or 
by one which is not sufficiently ductile at low temperatures. 

Produced by too small a percentage of bitumen in the surface. 

Produced by the use of an unsuitable bitumen. 

Produced by an unsuitable mineral aggregate. 

Produced by lack of compression. 

Produced by lack of traffic. 

Produced by sudden changes in temperature. 

Produced by vibration of rails, manholes and valve-boxes. 

Cracking of Asphalt Surfaces. — Cracks in the hydraulic con- 
crete base are at times reproduced in asphalt surfaces, even when 
the latter are of the best quality. The causes of cracks in base of 
this description must be referred to defects in the cement of which 
it is made, some of them expanding or contracting for some years 
after their use. Cracks due to this cause may be directly across 
the street or run in zig-zag directions along the crown and else- 
where, as shown in the illustration, Fig. 1, where cracks in the 
surface have been cut out to show those in the base. This form of 
cracking occurs both with natural and Portland cement, and with 
the very best surface mixtures under traffic, as well as with inferior 
ones under no traffic. 

If the cracked portions are renewed after the cement has attained 
volume constancy with age and the surface repaved, the cracks 
do not return. They are not a common form of defect in an 
asphalt surface. 

Cracks of the second description, due to the use of asphalt 
cement which is too hard or which has become hardened by being 
mixed with too hot sand, or to this cause combined with others, 
are the form which is most commonly met with. They are fre- 
quent in the hard Bermudez pavements laid in the Central States 
in 1898 and 1899, where the work was done according to a formula 
suitable for the materials available in 1893, but which with changed 
conditions resulted in later years in an asphalt cement of great 
hardness. Intelligence or proper supervision would have detected 
the unsuitable consistency of the cement. The results indicate 
the danger of following a blind formula. 

Such cracks are of course due to the fact that the hard asphalt 



DEFECTS AND DETERIORATION. 



481 



is too brittle at low temperatures to yield to the contraction of 
the surface It fractures under the tensile stress imposed upon it. 

An actual measurement of the contraction of an asphalt 
surface made by Mr. E. C. Wallace, formerly Chemist of the 
Warren-Scharf Asphalt Paving Company, outside the window 
of his laboratory during cold winter weather, has shown that above 
32° F. it is less than the average contraction of steel, and below 
freezing greater. This contraction is about that of quartz, and as 
quartz or similar mineral matter forms nearly 90 per cent of the 
mixture such a contraction would be expected. 

Determinations of the coefficient of expansion of various 
materials have been collected in the following tables from the 
literature of the subject, and a few determinations made by the 
writer are given for that of residuum and asphalt cements. 

COEFFICIENTS OF LINEAR EXPANSION FOR 1° C. 



Substance. 


Temperature. 


Coefficient. 


Authority. 


Quartz, mean 


0°-100° C. 

0°-100° c. 

0°-100° c. 

0°-100° c. 
100°-101° c. 

0°- 16° C. 
16°- 38° C. 
10°- 26° C. 
26°- 31° C. 

14°- 27° C. 
23°- 38° C. 

6°- 20° C. 
20°- 45° C. 


1,000,010.67 

1,000,011.80 

1,000,010.9 

1,000,095 

1,000,147 

1,000,106.6 

1.000,130.3 

1,000,230 

1,000,312 

1,000,989 
1,000,838.9 

1,000,544 
1,000,302 


Benoit 


tt « < 


Pulfrich 


Steel 


Benoit 


Petroleum, 26° B 


Sharpless 


<« a 


Parafline, hard 


Rodwell 


tt (i 


< < 


Beeswax 


Kopp 


1 1 


Eastern petroleum: 

Residuum, 21° B 




tt tt 


tt 


Bermudez asphalt cement 

100 asphalt, 20 residuum. . . 

a a a a 


tt 
tt 



The coefficient of expansion of petroleum residuum does 
not, like that of most oils, increase with rise in temperature, prob- 
ably due to the presence of paraffine, which solidifies at low tempera- 
tures and contracts rapidly. The bitumen of asphalt and asphalt 
cements contracts or expands in the same way. These results at 
first seemed rather startling, but reference to the literature of 
the subject confirms them. A paper by Holde in Mittheilungen 
der Konig, Technische Versuchsstation, 1893, 45-68, shows that: 



482 THE MODERN ASPHALT PAVEMENT. 

" The heavy viscous products of distillation or residues from 
crude petroleum of different origin, possessing a specific gravity 
of at least 0.908, do not show any marked difference in their expan- 
sions between +20° C. and 78° C. Their coefficient of expansion 
varies from 0.00070 to 0.00072. Those oils holding solid paraffine 
suspended at temperatures below +20° C. (as German oils) have 
a higher coefficient of expansion between 18° C. and 20° C, viz. 
0.00075 and 0.00081, owing to the melting of the solid particles. 

" The heavy liquid products of distillation, of specific gravities 
below 0.905, at + 15° C. possess a higher coefficient of expansion 
between 20° C. and 78° C, viz. 0.00072 to 0.00076. The American 
and Scotch oils belong to this class. 

"As to the completely fluid lubricating oils, their coefficients 
of expansion rise gradually in proportion to the increase of tempera- 
ture." 

In an asphalt surface one thousand feet long between —20° F. 
and 130° F., extremes of temperature that are met with by Omaha 
surfaces, the contraction of the sand alone, forming 90 per cent 
of the pavement, would amount to from .902 to .920 feet, or from 
10 to 11 inches. The contraction of the bitumen need not be 
considered, as this either elongates under the stress, or fractures. 
As low as 26° F. the elongation of a bitumen of proper consistency 
has been shown by experiments, to be described later, to take 
place quite readily. The contraction need therefore be considered 
only for the temperature between 26° and -20°, 46° F. or 25° C. 
For such an interval it would amount to about .29* of a foot per 
1000 feet, or about 1 inch in a Fifth Avenue, New York, block. It 
is not surprising, therefore, that with a hard cement rupture of the 
surface takes place, but rather that it does not always take place. 

The above conclusions are based entirely on theoretical consider- 
ations. Mr. S. Whinery and Mr. E. C. Wallace, of the Warren- 
Scharf Asphalt Paving Company, made some actual determinations 
some years ago of the expansion of an asphalt surface mixture on a 
laboratory scale. The means of measurement were not more 
accurate than 1/1000 inch. Using only those observations where 
the difference of temperature was 20° F. or more, and the expan- 



DEFECTS AND DETERIORATION. 



483 



sion or contraction, therefore, so considerable that it could be 
measured in this way with a fair degree of accuracy, they arrived 
at results which seem to be worthy of some confidence. There 
were four series of these observations, and the results are given 
in the following table. 



COEFFICIENT OF EXPANSION BY HEAT OF SHEET ASPHALT 
PAVEMENT. FROM OBSERVATIONS MADE BY LABORATORY 
OF THE WARREN-SCHARF ASPHALT PAVING COMPANY. 



Series. 


No- of Observa- 
tions Used. 


Mean Coefficient 
of Expansion. 


A 


13 

17 

12 

9 


.0000135 
.0000140 
.0000139 
.0000131 


B 


C 

D 





As the coefficient of expansion of structural steel is about 
.0000065, it is nearly correct to say that the coefficient of 
expansion of asphalt surface mixture as determined in this way is 
double that of steel. 

These results are about half of that which is arrived at theo- 
retically. What weight can be given to the results is some- 
what doubtful, but they are quoted here for what they are 
worth. 

Cracks which are due to the fact that the mixture is deficient 
in bitumen, in consequence of which the surface does not possess 
sufficient tensile strength, regardless of ductility, at low winter 
temperatures, are not as frequent as those due to a hard bitumen, 
since in such a mixture, disintegration with the formation of 
holes takes place, as a rule, before cracking. 

Cracks may be caused by the use of an asphalt cement which 
is unsuitable for the purpose to which it is applied. It may be 
too susceptible to temperature changes, so that, even if made so 
soft that the surface marks badly under a summer sun, it may 
be brittle at zero. 



484 THE MODERN ASPHALT PAVEMENT. 

Finally, an asphalt cement may so harden with age that it 
becomes brittle in the course of a few years. Coal-tar is an 
example of such a material. 

Cracking may be caused even with the most satisfactory asphalt 
cement by an unsuitable sand or mineral aggregate. Sands are 
known and have been used, the surface of the grains of which 
are of such a nature that melted asphalt cement will not adhere 
to them in sufficient thickness, and the voids in which are so small 
as to prevent the mixture from holding enough bitumen to give 
the pavement ductility. The sands available in other cities, 
without appreciable difference from those in use elsewhere, pro- 
duce a surface which never cracks, even under unfavorable con- 
ditions and inferior workmanship. 

Too fine a mineral aggregate may be a disadvantage on streets 
of little or no traffic. 

Lack of density in the surface also favors cracking, whether 
brought about by insufficient compaction when the surface is 
laid or subsequent lack of traffic. 

Traffic and the lack of it play a large part in preventing or 
causing the cracking of pavements. 

Traffic releases tension to a large degree in a cold asphalt sur- 
face and assists elongation of the bitumen, so that heavy-traffic 
streets do not crack as readily as those of light or no traffic, and 
oftener crack only in the gutters, if at all, while light-traffic streets 
crack entirely across the roadway. 

Suburban streets, not benefited by traction, at least in certain 
cities, are much more liable to crack than those which have a 
medium traffic. This is particularly well illustrated in a Canadian 
city where surfaces with only 8 to 9 per cent of bitumen are free 
from cracks on the downtown streets but are a mass of cracks 
in the suburbs, the bitumen present not being sufficient to give 
any elasticity unless the tension produced by contraction is 
released by traffic. 

Climate, of course, plays a large part in determining the fre- 
quency of cracks in asphalt surfaces. Mixtures of almost identical 
composition will fracture under the conditions met with in one 



DEFECTS AND DETERIORATION. 



485 



city and not in another. In those cities in the Missouri valley 
where sudden changes in temperature reaching 60° in a few hours, 
from 40° above zero to 20° below, cracking frequently results, 
w r here the same changes occurring more slowly in more protected 
locations do no damage. 

Cracking along rails and around boxes and manholes is due 
to lack oi support and may occur with the best mixtures. The 
causes have been considered elsewhere. 

In all of the causes of cracking which have been cited, except 
the last, laboratory investigations have thrown some light on the 
subject and the results obtained are of interest. 

Strength of Asphalt Surfaces. — An asphalt surface having the 
least ductility and tensile strength will, of course, rupture most 
readily under the tensile stress produced by contraction due to 
a fall of temperature. The tensile or crushing strength of an 
asphalt surface is, of course, a function of the temperature being 
greater at low than high temperature. Following are illustrations : 

FIFTH AVENUE, NEW YORK. LAID IN 1897. 



Temperature. 



6° F. 



38° F. 



76° F. 



Pounds per square inch: 
Tensile strength .... 
Crushing " .... 



880 
4862 



568 
2836 



300 
1820 



In considering the subject of cracked pavements our interest 
is entirely in the strength and ductility of the surfaces at low 
temperatures. 

From a great many old surfaces, some of which had cracked 
and some of which were free from them, briquettes were made 
and broken at 6° F. Averages of these determinations for the 
cracked and good surfaces in two cities are as follows: 



486 THE MODERN ASPHALT PAVEMENT. 

TENSILE STRENGTH IN POUNDS PER SQUARE INCH AT 6° P. 

No. 1. 

Cracked pavements 664 (6) 

Good " 722 (2) 

No. 2. 

Cracked pavements 497 (2) 

Good " 614 (6) 

There is a striking difference in the strength of the cracked 
and the good pavements in both cities in favor of the latter. 

It is of interest in this connection to know what peculiarities 
contribute to the strength of asphalt surfaces. Experiments have 
shown that the principal conditioning elements are: 

Asphalt Cement. 

Character. 

Consistency. 

Amount. 
Filler. 

Amount. 
Sand. 

Grading. 
Density of the surface. 

This subject was looked into to a considerable extent by the 
writer in 1894. Unfortunately this work was done with the 
old coarse Washington surface mixture. With the modern well 
graded New York material more satisfactory results would now be 
obtained. The experiments suffice, however, to bring out several 
points. Following are the available data. See table on page 487. 

These results show that the character of the cementing material 
has a very decided influence on the crushing, and it would also be 
found to be the same on the tensile strength of the surfaces. This 
subject was thoroughly discussed by the writer in a letter in the 
Engineering News for June, 1894, and it need only be said here 
that the strongest mixture is not the best, without regard to the 
nature of the bitumen, but that, with a proper cement, weakness 



DEFECTS AND DETERIORATION. 



487 



EFFECT OF THE CHARACTER OF THE BITUMEN ON THE 
CRUSHING STRENGTH. 

Crushing Strength of Mixtures of Coal-tar, Trinidad Lake and 

Land, Bermudez, and Pedernales Asphalt. 

Pounds per Square Inch. 



Mixture. 


Density. 


At 38° F. 


At 77° F. 


Coal-tar, 15% 


2.16 
2.07 
2.13 
2.10 
2.06 
2.14 


3880 
3845 
1813 
1955 
2125 
1375 


1254 


10% 


2655 


Land pitch cement, 15% or 10% bitumen 

Bermudez cement, 10% or 10% bitumen 

Pedernales asphalt, 10% or 10% bitumen 

Lake pitch cement, 15% or 10% bitumen 


761 
635 
550 

548 



Ten per cent of dust and Washington sand in all mixtures. 

at low temperatures due to ductility or elongation is preferable 
to high strength; weakness due to lack of bitumen, on the contrary, 
is not. 



EFFECT OF THE CONSISTENCY OF ASPHALT CEMENT ON 
STRENGTH OF SURFACES. 

Washington Mixture, 1894, Pounds per Square Inch. 



Softness. 


Crushing Strength. 


Shearing Strength. 


36° F. 


77° F. 


36° F. 


77° F. 


Trinidad cement: 

Normal consistency 


1703 
1610 

2416 
3028 


680 

682 

741 
602 


2865 
2005 

3193 

2569 


1425 


Softer cement, 3 lbs. more oil 

Bermudez cement: 

Normal consistency 


1873 
1528 


Softer " 


1876 







These results show that a softer Trinidad cement makes a 
mixture which has, owing to its great ductility, a smaller crushing 
strength at 36° than the one made with a hard cement; but with 
Bermudez cement this is not the case, as this cementing material 
is more easily affected by a fall of temperature. 

With a better sand grading, however, the above results might 
be somewhat modified. 



488 



THE MODERN ASPHALT PAVEMENT. 



EFFECT OF THE QUANTITY OF ASPHALT CEMENT ON 

STRENGTH OF SURFACES. 

Washington Mixture, 1894, Pounds per Square Inch. 



Amount. 


Crushing Strength. 


Shearing Strength. 


36° F. 


77° F. 


36° F. 


77° F. 


Trinidad cement: 

Normal 15% 


1703 

2425 

2416 

2544 


880 
768 

741 
961 


2865 

2882 

3193 
2511 


1425 


More cement 16.5% 

Bermudez cement: 

Normal 10% 


2378 
1528 


More cement 11% 


1636 



These results show that an increase in the amount of asphalt 
in a mixture, up to a certain point, increases the strength of a 
Trinidad mixture in all cases; but, as before, not always, with 
Bermudez asphalt due to differences in the physical properties of 
the two bitumens at low temperatures. 

EFFECT OF INCREASE OF AMOUNT OF DUST IN SURFACE 

MIXTURES ON THEIR TENSILE STRENGTH. 

Pounds per Square Inch. 



Dust 
per Cent. 


Trinidad 
at 36° F. 


Bermudez 
at 36° F. 


Trinidad 
at 77° F. 


Bermudez 
at 77° F. 


7.5 
10.0 
15.0 
20.0 


501 
604 

646 
701 


449 

611 
662 

857 


188 

205 
273 
270 


Ill 

171 
186 
192 



The addition of increased amounts of dust gives decided evi- 
dence of improvement of. the mixture in all cases, and shows the 
necessity of using plenty of filler. 

EFFECT OF DENSITY ON STRENGTH OF SURFACES. 



Compaction. 


Tensile Strength at 

40° F. | 77° F. | 90° F. 

Pounds Per Square Inch. 


Density. 


Least dense 


463 
646 


152 
273 


101 
166 


2.08 


Densest 


2.23 







DEFECTS AND DETERIORATION. 



489 



The above results show that there can be no doubt that the 
densest mixtures are the strongest, at least with the same mineral 
aggregate and a sufficient amount of bitumen. 

EFFECT OF SAND GRADING ON STRENGTH OF SURFACES. 
Washington and New York. 





Bitu- 
men. 


Passing. 


Composition. 


200 


100 


80 


50 


40 


30 


20 


10 


New York . . 
Washington. 


10.6 
10.5 


14.4 

9.7 


11.0 

3.2 


12.0 
5.4 


27.0 
22.3 


11.0 

20.5 


7.0 
13.2 


4.0 

7.8 


3.0 

7.4 



TENSILE STRENGTH, POUNDS PER SQUARE INCH. 





At 38° F. 


At 78° F. 


New York 


568 lbs. 
604 " 


300 lbs. 
205 " 


Washington 





The difference between the fine and coarse mixture at 36° F. 
is slightly in favor of the coarse; at 78° F. in favor of the fine. 

It must be remembered, however, that in these tests there 
are a number of conditions beside the grading of the sand that 
enter into the problem, so that final conclusions can hardly be 
drawn from so few experiments. 

As a whole the results of these physical tests throw considerable 
light on the peculiarities of mixtures of varying composition and 
give us some information as to why some crack and others do not. 

The possibility of cracking in asphalt surfaces are seen to 
be large, and it is remarkable how well they have been overcome 
by intelligent study of the conditions that are to be met. There 
is still much to be learned in this direction. It is impossible, as 
yet, to say why cracking has never occurred in pavements, even 
when not laid with the greatest care, in one city, while they are 
of general occurrence in another where the greatest care is exer- 
cised. It must, of course, be due to peculiarities in the surface 
of the grains of the sands in use, and the relative degree of 
adhesion of asphalt to them. 



490 THE MODERN ASPHALT PAVEMENT. 

Cracks are never known to heal. Experiments have shown 
that an asphalt contracts longitudinally, but expands vertically, 
bo that cracks once formed increase in width every winter, not 
only for this reason but because they become filled with dirt. 

Cracks may be merely unsightly or they may be the essential 
cause of subsequent disintegration. 

Asphalt surfaces on suburban streets in some climates crack 
to a marked degree after about three years service; but if the sur- 
face mixture is a good one, no disintegration follows and the pave- 
ment continues to be satisfactory in every other respect for as 
long a period as if no cracks existed. If disintegration takes 
place in such cases it is due to inferiority in the character of the 
mixture. There need be no alarm if no disintegration sets in. 
If local prejudice against a very soft surface which marks excessively 
when first laid does not exist, cracks may be largely avoided by 
using a very soft asphalt cement in the surface. In a north- 
western city, where no asphalt surface had ever been laid on a 
residence street without cracks appearing in a few years, this was 
avoided in some laid by the writer by using a cement of 90 to 
100 penetration insead of one of 65, as had been previously the 
case. The surface marked up under traffic excessively, however, 
during the first summer and aroused much comment. Com- 
munities soon become accustomed to this and the marking in 
new surfaces is objected to no longer, as it is understood that the 
pavement will eventually be a superior one. In consequence, 
much of the cracking of asphalt surfaces can now be avoided 
if they are originally laid with sufficiently soft bitumen, and the 
reason for the ensuing marking is properly explained to the public. 

Disintegration. — Disintegration of the surface in various parts 
with the formation of depressions or holes extending to the base 
is the commonest defect in asphalt surfaces. Many defects of 
this kind are attributable to faults of construction, but they may 
also be due to unfavorable environment with the best of surface 
mixtures. Altogether they may be summed up as: 

Deteriorations or defects due to: 

Weak foundation — an extremely common cause. 

Inferior mixture. 



DEFECTS AND DETERIORATION. 491 

Action of illuminating-gas. 

Action of water. 

Uneven thickness of surface and constant pounding on depres- 
sions in an unbalanced mixture. 

Weak Foundation. — An asphalt surface cannot resist the impact of 
traffic if the foundation does not furnish adequate support. This, as 
has been reiterated many times in these pages, is one of the most seri- 
ous causes of the deterioration of asphalt pavements in large cities 
and where they are subject to heavy traffic and moisture. Any 
vibration in the surface, especially under unfavorable surface con- 
ditions such as dirt and continued moisture, is extremely liable to 
result in deterioration of a poor mixture and will aid in destroying 
the best surface. A defect due to weak foundation may be manifest in 
many ways. The surface may merely break up and go to pieces, 
or it may at first merely separate into small individual masses 
which become rounded at their edges and form a collective group 
of almond-shaped patches, which eventually go to pieces with a 
resulting hole. 

Inferior Mixture. — Disintegration due to inferior mixture has 
been too thoroughly discussed in previous pages to necessitate 
a recurrence to the reasons therefor. It is, of course, in careless 
work the chief cause of defects in asphalt surfaces, but too often 
disintegration is attributed to a poor mixture which is due entirely 
to other causes. 

Action of Illuminating-gas. — The disintegrating effect of the 
action of illuminating-gas is a subject which has not been consid- 
ered hitherto in these pages. * The writer cannot do better than 
by allowing Mr. A. W. Dow, his successor in the Office of Inspector 
of Asphalt and Cements, in the District of Columbia, to speak of 
his experiences in Washington with this cause of deterioration of 
asphalt surfaces, as all that he says applies as well to other cities. 
He writes as follows in his report to the Engineer Commissioner 
of the District of Columbia, for the fiscal year ending June 30, 
1899: 

"Disintegration of pavements from the absorption of illuminat- 
ing-gas, escaping from leaky gas-pipes or mains under the pave- 
ment: There are several streets in the city being ruined by this 



492 THE MODERN ASPHALT PAVEMENT. 

means, and it appears to be a common thing in all cities having 
gas. 'The pavements are affected in very much the same way as 
when disintegrated by coal-tar binder, except the fine cracks, 
running parallel with the street, make their appearance sometime 
before the pavement begins to crowd. Pieces of the surface 
mixture taken up smell very strongly of illuminating-gas, and in 
some cases the gas can be ignited by applying a match to the under 
surface when it has just been taken up. In nearly every case 
enough gas will be given off by heating a small piece of the affected 
pavement in a tube to have it flash by igniting. 

" As it has been doubted by some that this disintegration is 
really due to illuminating-gas, I have made a most thorough investi- 
gation of the subject and believe have positively proven that 
gas is the cause. Samples of pavements were obtained from 
several affected spots, and in all cases I have been able to obtain 
from them a gas that exploded by passing an electric spark after 
mixing with air. The method employed to obtain the gas from 
samples of the surface mixture was by heating them under boiling 
water and collecting the gas given off in an inverted funnel. Those 
not acquainted with the properties of asphalts might suggest that 
heating any asphalt to this temperature might make it give off a 
gas. This is impossible, as an asphalt cement such as is used in 
paving will lose only 3 or 4 per cent at the most on being kept at 
a temperature of 400° F. for 30 hours, and only an infinitesimal 
part of this loss is a gas at ordinary temperatures. To make a 
more practical demonstration of this, two samples of a pavement 
were taken, one from an affected spot and the other from a good 
portion of the pavement about 10 feet away. These samples 
were treated under boiling water until they ceased to evolve gas. 
The affected sample gave several times more gas than did the other. 
On testing, the gas from the good sample was found to consist of 
oxygen and nitrogen, which was evidently just the air from the 
voids of the pavement. The gas from the affected piece gave on 
analysis : 



DEFECTS AND DETERIORATION. 493 

Carbon dioxide 8 . 4% 

Oxygen 10.8 

Heavy hydrocarbons 13 .4 

Carbon monoxide. 0.7 

Hydrogen 6.6 

Methane 2.0 

Nitrogen 58 . 1 



t( 



Having now found that a gas is present in the pavement so 
affected, let us proceed to examine as to its source. It cannot be 
a natural gas or marsh-gas, for there is no analysis of such gases 
on record that contains appreciable amounts of heavy hydrocar- 
bons, while the gas from the pavement is rich in these compounds. 
The same would also apply to sewer air or gas. The only 
remaining source is illuminating-gas, the analysis of 'which is 
here given: 

Carbon dioxide . 2% 

Oxygen 0.0 

Heavy hydrocarbons 12. 1 

Carbon monoxide , 25 . 5 

Hydrogen 39.2 

Methane 23 .0 

Nitrogen 0.0 

" On comparing the composition of the gas given off from the 
disintegrating pavement with the illuminating-gas it is seen that 
they are not at all similar in composition. At first glance it would 
not seem possible that the former gas could originate from the 
latter, but when the properties of asphalt are considered it is easily 
explained. 

" Heavy hydrocarbons, to which class asphalts belong, are 
known to absorb other gaseous hydrocarbons ; the heavier the gas 
the more affinity between it and the heavy hydrocarbons. Know- 
ing this, the ingredients of the illuminating-gas that asphalt would 
have the greatest affinity for would be the heavy hydrocarbon 
gases, a slight affinity for tlie marsh-gas or methane, and no affinity 
for any of the other ingredients. If we examine the ingredients 
of the gas from the affected pavement, it will be found to consist 
of some carbon dioxide, air that was in the voids and cracks of the 
pavement, and the constituents of illuminating-gas with the heavy 



494 



THE MODERN ASPHALT PAVEMENT. 



hydrocarbon gases very much in excess, which is what we woulit 
expect. To practically demonstrate that the above takes place 
when asphalt is in contact with illuminating-gas , I took two samples 
of gas from a tap in the laboratory. One was analyzed, while the 
other was kept for several weeks in a tube the interior of which 
was coated with asphalt cement such as is used in pavements, 
after which it was analyzed. The results of the two analyses are 
here given : 



Carbon dioxide 

Oxygen 

Heavy hydrocarbons 
Carbon monoxide. . . 

Hydrogen 

Methane 

Nitrogen 



Original 



0-2% 

0.0 
12.1 
25.5 
39.2 
23.0 

0.0 



Gas after 

Asphalt 
Absorption. 



o.i% 

0.0 

7.2 
27.3 
42.2 
23.2 

0.0 



" It is evident from this that the asphalt cement has absorbed 
over 5 per cent of the heavy hydrocarbon gases, a little methane, 
and practically nothing else. 

" I have ascertained by experiment that one part by volume 
of asphalt cement will absorb forty-two parts of illuminating- 
gas in somewhat over a month. I have also practically shown 
that asphalt is much softened by asborbing gas, the ordinary 
asphalt cement becoming as soft as a thick maltha after being in 
an atmosphere of illuminating-gas for several months. As to the 
quantity of gas contained in the affected pavements this of course 
varies, but in one instance 1000 c.c. of pavement gave off 500 c.c. 
of gas. 

" There is but one way to stop the disintegration of a pave- 
ment from this cause, and that is to stop the leak of gas; for it 
is useless to patch the pavement, as it will not be long before 
the patch disintegrates. I have known of cases where a pave- 
ment so affected was repaired and in fourteen months the patches 
were showing signs of disintegration." 

The writer's investigations have in every respect confirmed the 
conclusions of Mr. Dow. 



DEFECTS AND DETERIORATION. 495 

Water Action. — The action of water on poor and unsatisfactory- 
asphalt surfaces has also been considered at length. Continued 
standing or running water will destroy the best asphalt surface, but 
such a defect is one which can be avoided by proper provision for 
the prevention of such conditions. The best surfaces will resist for 
years any reasonable water action. Unfortunately provisions for 
preventing such action are not always adequate either from the 
presence of a porous base, seepage from soil in terraces above the 
level of the base, or poorly arranged grades to the actual surface 
of the pavement, which permit water to stand in the gutters. These 
defects, not inherent in the pavement but merely in the mode of 
construction, can be readily provided against. 

Of the results of the action of water reaching the asphalt through 
a porous base, Mr. A. W. Dow writes as follows: 

" Disintegration by Water Entering a Pavement by Oozing up 
Through the Base. — I believe if more thorough investigation were 
made into the cause for the disintegrating of pavement, this would 
be found to be one of the most common, especially in small towns 
and cities where there are terraces or considerable lawns in front 
of houses. There have been a number of cases in this city where 
the water has entered a terrace or parking where they were above 
the grade of the street and worked its way up through the con- 
crete base to the asphalt surface. 

" This disintegration manifests itself differently, depending 
on the character of the pavement. If the asphalt surface is soft 
or the concrete smooth, the first defect noticed will be the ten- 
dency of the pavement to crowd in warm weather. This is due 
to the under portion of the surface mixture rotting, so to speak, 
thus destroying the cementing properties of the asphalt. The 
upper portion, although good, being deprived of the support of 
the affected mixture under it, will be crowded out by traffic. This 
crowding is assisted by the concrete base being smooth, and also 
the bond between the base and binder are destroyed by the moisture. 

" In cases where the concrete base is rough and the surface 
mixture hard, the principal disintegration will take place in cold 
weather, nothing abnormal being noticed until the pavement 
begins a rapid crumbling away in the affected spots under traffic. 



496 THE MODERN ASPHALT PAVEMENT. 

" On examining a section of asphalt surface disintegrating 
from this cause, especially where it has not been going on for 
too long a time, there will be found a layer of perfectly sound 
and good material at the surface of the pavement, while under- 
neath the mixture will show evidence of being disintegrated by 
water — that is, the sand will appear clean and white in spots, as 
though there had been an insufficiency of asphalt cement to cover it. 
The concrete base under the affected pavement will generally 
be found damp or even wet. We have prevented the destruction 
of several pavements from this cause by the use of blind drains 
put in under the gutter next to the lawn or terrace, and even 
run herringbone under the pavement. 

" This last cause for disintegration would, of course, not occur 
in a pavement constructed with an asphalt that was unacted 
on by water, but water soaking up through a concrete base might 
injure any pavement by freezing. 

" It is always advisable where a pavement shows signs of dis- 
integrating to examine into the cause in a most careful manner 
and not pass snap judgment. It seems only too easy for the 
majority of people, whether experienced or not, to place the blame 
for the failure of a pavement on the manufacturers. I have heard 
men with considerable experience, commenting on a bad place 
in a pavement that they had not carefully examined, remark, 
' They used bad oil or asphalt in that piece of work.' They have 
not taken into consideration that all but possibly a square yard 
of the pavement is in good condition and that it would be no 
economy to a contractor to use -bad material in one small place 
of the pavement. A careful examination into the disintegrating 
of a pavement may, in many cases, show a cause that is entirely 
foreign to the composition of the materials and a cause that could 
be easily remedied with a little common sense." 

The conclusions of Mr. Dow in regard to such causes of dis- 
integration are most reasonable. 

Poor Workmanship. — The raking of the hot asphalt mixture 
to an uneven thickness before compression, resulting in the forma- 
tion of depressions in the surface under the final compression 
obtained from traffic results in disintegration of the less satisfactory 



DEFECTS AND DETERIORATION. 497 

mixtures owing to the constant impact of the wheels of vehicles 
suddenly dropping into such depressions. This is a fault often due 
to carelessness in construction and is not a common one. 

Scaling of Asphalt Surfaces. — Scaling of asphalt surfaces has 
been in individual cases a serious cause of the deterioration. It is 
something which happens only in moist climates, particularly in 
those near the seacoast, or where fogs are prevalent, and where it 
is the custom to water streets continually without the removal of 
the accumulated dirt. It is particularly frequent with coarse 
mixtures, and in order to avoid it the grading of the sand, the 
character of the filler, the character of the asphalt and flux in use, 
their proper combination, together with the support of the resulting 
surface on a base free from vibration, must receive the most care- 
ful attention. 

That the problem can be successfully met has been proved by 
the fact that pavements which have not suffered from scaling 
have been laid on Broadway and Fifth Avenue in New York, and 
in the foggy and damp climates of London, Glasgow, and Paris, 
in the first of which cities the successful application of the modern 
asphalt surface mixture was worked out in 1896 after two failures, 
to be equally successfully followed by similar results later in Glas- 
gow and Paris. 

Scaling is characterized by the separation under traffic, when 
the streets are wet and the air so humid as to prevent their drying, 
of a thin film of the asphalt mixture from the surface of the pave- 
ment. No satisfactory explanation of this phenomena has been 
advanced. We must content ourselves with noting its occurrence. 

After drying out the asphalt surface resumes its normal appear- 
ance, rolling out smoothly under traffic, but the thickness of the 
pavement is decreased. The same thing will happen again under 
like conditions until a depression or hole is worn and repairs are 
necessary. 

Enough is known, as has been said, to show that the weaker 
poorly graded mixtures lacking in bitumen and made with unsatis- 
factory asphalt cement suffer most from scaling. It is also much 
more in evidence where the base is weak. Mixtures having a filler 
of Portland cement are the most resistant, and finally it never 



498 THE MODERN ASPHALT PAVEMENT. 

occurs in a pavement thoroughly well constructed, such as that 
on Fifth Avenue in New York, or those properly laid in London 
and Paris; that is to say, it can be avoided entirely if the proper 
precautions are used. The watering-cart and lack of cleanliness 
are great aids to the production of scaling and, in fact, to the 
general diminution of the life of an asphalt pavement, but this is 
a condition the consideration of which must properly be taken up 
under the head of the effect of environment upon such surfaces. 

Displacement of Asphalt Surfaces. — The displacement of 
asphalt pavements under traffic resulting in a rolling or wavy 
surface was a serious defect in the early days of the industry. 
It was due to the fact that the asphalt mixtures were unbalanced, 
the mineral aggregate was not properly graded, and the bitumen 
was present either in too small or too great an amount, with the 
result that the surface, not having sufficient internal stability, 
moved upon the more or less smooth hydraulic base, to which it 
was not tied by any intermediate course, under the pressure and 
impact of traffic. It has even moved in cases where such a course 
exists where the stability is unusually small. Defects of this 
description, which were at one time common, have been avoided 
not only by the introduction of a binder or paint course, but also, 
in the few surfaces constructed in recent years without such a 
course, by the greater stability of the surface mixture. 

Displacement of the surface and formation of waves in asphalt 
surfaces do, however, occur occasionally at present, and this 
has been found to be due to the percolation of water through an 
open binder course, and its attacking the under surface of the 
wearing surface of the pavement, thus reducing its stability and 
permitting of the movement of the upper portion of the surface 
upon the loosened lower part. This occurrence is particularly 
noticeable where a pavement of this form of construction adjoins 
a street railway track which is not stable, vibrating and admitting 
water fr^ween the rail and the pavement. Such occurrences 
bring out very strongly the injury to all forms of pavement, of 
an unsatisfactory track construction, and of the difficulty of 
maintaining any pavement under such conditions. 



DEFECTS AND DETERIORATION. 499 

Expansion of Cement in the Foundation. — The surface of an 
asphalt pavement has been at times raised transversely into waves 
by the expansion of the cement used in the construction of the base 
with the direct result of raising the latter at points of least resist- 
ance generally at joints between different days' work and the 
immediate elevation of the asphalt surface above these points. 
This has occurred with both natural and Portland cement, but 
usually with magnesian cements of the former type. When the 
expansion has ceased after the lapse of several years, removal of 
the excess of base and replacement of the surface at a normal 
grade obviates any further trouble. 

Deterioration of Asphalt Pavements Due to Environment. — 
Deterioration in asphalt surfaces is brought about, even in those 
of the best form of construction, or to a much greater degree, of 
course, in those which are poorly constructed, by the nature of 
the environment to which they are subjected. 

Difficult climatic environment is something that cannot be 
escaped and must be met as well as possible by the form of con- 
struction of the pavement and by the character of the surface 
mixture with which the pavement is constructed. That this 
must be accommodated to the climatic conditions which it is 
to meet is apparent and is generally understood, at least as far 
as temperature in its relations to latitude is concerned and with 
reference to sudden falls in temperature. The unfavorable envi- 
ronment due to prolonged humidity is, however, the most serious 
condition to be met, especially ^here the traffic is heavy, the sur- 
face not kept clean, and the air temperature for long periods lying 
between freezing and 45° F. As examples of the former con- 
dition might be cited the climate of St. Paul, Omaha, and New 
Orleans. 

In the latter place it is very necessary to make the surface 
with a bitumen sufficiently hard in consistency not to prove unde- 
sirable in the summer months, as the temperatures in winter are 
not low enough to produce cracking. For this purpose a cement 
of 50 penetration on the Bowen machine is usually employed. 
In St. Paul, on the other hand, where the winter temperatures 
are very low a penetration of 90 is used. A cement of this degree 



500 THE MODERN ASPHALT PAVEMENT. 

of softness will naturally result in a pavement which marks up 
to a notable extent in the summer when first laid, but this dis- 
agreeable feature disappears after the second winter, and such a 
surface does not crack as would those laid with a harder cement. 

A still more difficult climatic feature to meet is that of sudden 
drops in temperature, often as much as 50° in a few hours, which 
are met with in cities like Omaha. The immediate contraction 
caused by such a drop is so great as to. overcome the elasticity 
or ductility of the bitumen, and cracking can only be prevented 
by using in the mixture as it is originally laid a very soft asphalt 
cement. An example of such a surface, that laid on Thirty-ninth 
Street in Omaha, Neb., will serve. It was so soft when it was 
completed and marked so freely that it was not at once accepted 
by the city. To-day it is the only pavement of its age in that 
city which has not cracked and now does not mark exceptionally 
under the hottest summer suns. 

Experience has taught fiow these difficulties may be met with 
in the manner described, but pavements constructed by an inex- 
perienced contractor, with an unbalanced mineral aggregate which 
will not permit the use of cement of sufficiently soft consistency, 
will inevitably show cracks in a colder climate in the course of 
two or three years. 

A still more serious climatic condition to contend with is that 
met with in climates where there is excessive humidity in the winter 
months. Where such a condition exists only the most carefully 
prepared surface mixture will resist the combined action of moisture 
and heavy traffic. This was well illustrated in the earlier attempts 
to lay asphalt pavements in London, Glasgow, and on the north- 
western Pacific Coast. It is even met with in some of our cities 
on the Atlantic Coast where asphalt pavements are placed on 
very heavy-traffic streets. Much of the earlier scaling in New 
York City was due to humidity combined with temperatures 
between 45° and the freezing-point. Below a freezing tempera- 
ture scaling and disintegration due to this cause does not take 
place. 

The deterioration of an asphalt pavement caused by the unfavor- 
able environment produced by the leakage of coal-gas from gas- 



DEFECTS AND DETERIORATION. 501 

mains is an important one and has already been discussed under 
the heading " Disintegration." 

Attention has already been called to the fact that asphaltic 
paving mixtures will not withstand the constant action of ground 
or running water, and where they are subjected to such an environ- 
ment they will inevitably deteriorate more rapidly than is necessary. 
The remedy for defects clue to the constant action of water is 
the removal of the cause by the introduction of proper provisions 
for drainage. 

Asphalt pavements also suffer in one or two of our cities from 
flushing with water under a very considerable head with a hose 
and nozzle. No surface of any description can be expected to 
withstand such hydraulic mining. If it is carried on the city 
must expect to have the cost of maintenance of its asphalt streets 
much increased at the end of the guarantee period, and this will 
be the greater the more inferior the asphalt surface mixture is 
in the beginning. 

A still greater cause of deterioration of asphalt pavements 
is found in the lack of cleanliness and general neglect. If the 
pavements are not carefully cleaned and filth is allowed to lie 
upon the surface for a great length of time, becoming mud as 
soon as they are sprinkled or rained upon, the deterioration is 
very rapid and even worse than when they are subjected to the 
action of clean water. Permitting mud and slime to remain upon 
an asphalt surface displays great ignorance, upon the part of pub- 
lic officials of the nature and behavior of asphalt pavements and 
should never be allowed to take place. For the same reason 
asphalt pavements should never be sprinkled if possible. The 
dirt should be removed and the situation not temporized with it 
by converting it into a slimy mud. This is doubly the case since 
such a slimy coating results in making the pavement extremely 
slippery, a feature not inherent in the asphalt surface itself, but 
attributable only to the film of mud. 

Finally, asphalt surfaces in cities like New York, suffer enor- 
mously from the constant disturbance to which they are subjected 



502 THE MODERN ASPHALT PAVEMENT. 

by being taken up in connection with underground work. Though 
an asphalt pavement can be repaired more readily than any other, 
its constant removal and renewal cannot but injure it, as the 
foundation in such cases is never as rigid as the original. It can 
be asserted without doubt that not only asphalt pavements, but 
all others in a large city, can never be kept in a state of perfect 
maintenance until pipe galleries are provided under the streets 
which shall do away with the constant opening of the surface. 
In some of the streets of New York, from one-third to more than 
the entire area of the street has been often renewed in the course 
of the guarantee period for this reason. 

Deterioration Due to Natural Wear and Neglect of Mainte- 
nance. — An asphalt surface is naturally more or less deteriorated 
by usage, like all materials of construction, and the amount which 
it suffers in this respect depends entirely upon the character of 
the original workmanship and the traffic and other conditions to 
which it is to be exposed. Some asphalt pavements under 
light traffic, such as that opposite the Arlington Hotel in 
the city of Washington, have given good service for 30 years 
and may be expected to last much longer. On the heaviest 
traffic streets constructed with the greatest skill some minor 
repairs may be expected at the end of from 3 to 5 years, depend- 
ing upon the rigidity of the base which supports the surface 
and upon the manner in which these repairs are made, the 
extent of its deterioration will largely depend. The question of 
maintenance will be discussed in the following chapter. 

SUMMARY. 

To the general reader the preceding chapter will probably be 
one of the most interesting and instructive in the book, and it should 
be read in detail, as it explains the reasons for defects in and the 
causes of the deterioration in asphalt surfaces. The chapter may be 
summarized briefly as follows : 

Defects in asphalt pavements are, to the greatest extent, to be 
attributed to faults of construction. 



DEFECTS AND DETERIORATION. 503 

1. Due to improper specifications for the form of construction, 
the fault of the city officials. 

2. Due to careless construction on the part of the contractor, 
and also 

3. To improper maintenance when the age of the pavement is 
such that it should be given careful attention, as unfortunately 
the American public and many city officials seem to believe that 
when a street is once paved it should be expected to last forever 
without maintenance. 

4. The action of illuminating-gas escaping from the mains. 

5. Constant opening for underground work. 



CHAPTER XXVI 

MAINTENANCE OF ASPHALT PAVEMENTS. 

The question of the proper maintenance of asphalt pavements 
demands, but has not received, very careful consideration on 
the part of most of our municipalities and municipal officials, 
but it fortunately is receiving more to-day than in the past. Owing 
to the fact that asphalt pavements have generally been laid under 
guarantees by the contractor for their maintenance for a con- 
siderable period, a custom which, as has been said, 1 is rapidly 
disappearing, too little consideration has been given to their 
maintenance after its expiration. As a result of this, they have 
deteriorated very rapidly when thrown upon the hands of the 
municipality, and their condition has become such as to cause 
very unfavorable comment and great dissatisfaction. In a few 
cities, such as Washington, D. C, it has been demonstrated that 
there is no difficulty in maintaining an ordinary asphalt street 
in good condition for from 15 to 20 years, at a moderate cost, 
as has been shown by Capt. H. C. Newcomer in a report published 
in the Engineering News for February 18, 1904, where he shows 
that of the 2,425,732 square yards of bituminous pavements 
maintained by that city, of which not less than 2,161,181 square 
yards are laid with Trinidad Lake asphalt, the cost of main- 
tenance was as follows, the average age of the surfaces being 
about 14.8 years, while there are over 700,000 square yards that 
are over 18 years of age. He also shows that the average age 

1 See page 445. 

504 



MAINTENANCE OF ASPHALT PAVEMENTS. 



505 



of the areas resurfaced during the fiscal year ending July 1, 1903, 
was 21 years, and this may be regarded as well within the limits 
of the duration of a standard asphalt pavement, if it is properly 
maintained during the period, especially as the older mixtures 
laid in Washington were by no means up to the standard of ex- 
cellence of those which are now being put down. 

t!OST OF MAINTAINING ASPHALT PAVEMENTS OF VARIOUS 
AGES AT WASHINGTON, D. C. 



Age in Years. 


Area, 
Square Yards. 


Cost of Repairs 
for the Year. 


Average Cost pec 

Square Yard 

per Year. 


5 


1,841,435 

1,809,809 

1,747,461 

1,653,811 

1,597,313 

1,476,575 

1,292,200 

1,088,848 

913,795 

804,420 

698,826 

608,117 

500,823 

504,995 

374,800 

272,040 

192,643 

104,001 

33,332 

35,647 


$11,897 

13,965 

31,385 

38,531 

42,871 

38,500 

43,003 

42,270 

31,546 

28,435 

21,576 

23,479 

18,913 

23,012 

11,951 

7,182 

3,879 

2,887 

678 

1,208 


$0.0065 


6 


.0077 


7 


.0180 


8 


.0233 


9 


.0269 


1C 


.0200 


11 


.0333 


12 


.0396 


13 ;.. 


.0345 


14 


.0354 


15 


0309 


16 


.0386 


17 


.0338 


18 


0456 


19 


.0319 


20 


0264 


21 


0201 


22 


0280 


23 


0187 


24 


.0356 







Neglect of maintenance, however, has resulted in quite a 
different condition in many other cities. There are one or two 
cities in the United States where, at the expiration of the guarantee 
period, no attempt is made at further maintenance, and, as a 
result, the asphalt pavements in these cities in a few years are 
in a wretched condition, arousing; comment and adverse criticism 
of this form of pavement on the part of all the' citizens. This 
can in nowise be attributed to the character of the pavement 
itself, but to the narrow policy pursued by the public officials in 
charge of the streets. Nothing can be so far from economical 



506 THE MODERN ASPHALT PAVEMENT. 

as to allow an asphalt pavement to go without repairs when they 
are needed, as, in this case as in all others, a ' 'stitch in time saves 
nine." 

On the other hand, there are numerous cities, such as Phila- 
delphia and Washington, which have met with no difficulty 
whatever in maintaining their asphalt pavements in good condition 
under the contract system, a proper amount of funds being made 
available in the spring of the year. In at least one other city 
where the money is not available until mid-summer, July 1st, 
the contract system has not proved as desirable. In several cities, 
the failure of the contract system has been due more to the pro- 
miscuous way in which cutting up of the pavement is permitted 
by the city authorities, than to the manner in which repairs are 
made. 

This situation has been discussed, as far as maintenance is 
concerned, in an article by Mr. S. Whinery, in Engineering News 
for May 9, 1907. He says in part: 

"It cannot be denied that the condition of asphalt pavements 
in most cities is unsatisfactory, while in many it is deplorable and 
is rapidly becoming intolerable. To attribute this condition to 
inherent inferiority of this kind of pavement, as many people do, 
is wholly unwarranted. Everything considered, a well constructed 
and properly maintained asphalt pavement is not inferior to any 
other kind of pavement now in use. At the same time it must be 
conceded that an asphalt pavement usually requires attention and 
repairs at an earlier period in its life than most of the other pave- 
ments in common use, and it is probable, though not yet certain, 
that the total cost of maintenance during its useful life is also 
somewhat greater. It is certain that it requires more frequent 
and careful attention during its life to keep it in a proper state of 
repair than do stone or brick pavements. It is often the case 
that high grade articles or structures require more careful and 
skillful attention than the cruder varieties of the same class. 
It will certainly not be claimed that the value of a pavement 
may be measured by the amount of neglect and abuse it will 
endure." 

"As the first important step in this direction the city must 



MAINTENANCE OF ASPHALT PAVEMENTS. 507 

avoid, in the contract and specifications, requirements that are 
indefinite and ambiguous, and under which the contractor's 
duties cannot be clearly determined and enforced. We have 
seen that the long guaranty involves inherent conditions which, 
under the above stipulation, it is necessary to avoid. It should 
therefore be omitted from all future contracts. The art of con- 
structing asphalt pavements is now so well understood that it 
is entirely possible to frame and administer specifications that 
will insure the production of a first class pavement, and the con- 
ditions that originally dictated these guarantees therefore no 
longer exist. The attempt thus to make the contractor responsible 
for the character of the work he does has not, in practice, been 
found effectual; moreover, our present knowledge of how the 
work should be done and the practicability of thorough inspection 
and supervision, renders the resort to such an expedient largely 
unnecessary. But if a time guaranty is still thought advisable, 
the period may be made so comparatively short that questions of 
faulty construction shall not be confused with those of mainte- 
nance. Barring accidental and unusual injuries, maintenance 
questions ought not to arise within a period of two years after the 
completion of the construction work, while palpable construction 
faults should be revealed within that time. The guaranty 
period should not therefore, exceed two, or at the most, three 
years. Maintenance after that period shouM be provided by 
the city." 

Surface Heaters. — The question of the best way to maintain 
an asphalt pavement lies between cutting out the entire surface 
and binder, and the use of what are known as "surface heaters, 7 ' 
which consist of a machine which directs a blast of flame from a 
series of naphtha burners upon the asphalt surface and softens 
it so that it can be removed to such depth as may be necessary 
to reach undisintegrated material, and then applying sufficient 
fresh material upon the area thus laid bare to renew the pavement 
to proper thickness. Such work has been extremely satisfactory 
in the past. As an example, the surface of Madison Avenue, 
between 23d and 26th Streets, in New York City, was entirely 
replaced in this manner in 1895, and has remained in excellent 



508 THE MODERN ASPHALT PAVEMENT. 

condition up to the present time. Of course the work cannot 
be done in wet or cold weather. At such periods the entire sur- 
face where disintegration occurs must be cut out to the foundation. 
The surface heater work is of course much more ecouomical. 

Under any circumstances, all maintenance and repair work 
will require the greatest skill in their execution, and too much 
care cannot be devoted to the details of it. 



PART IX. 
CONTROL OF WORK. 



CHAPTER XVII. 

INSTRUCTIONS FOR COLLECTING AND FORWARDING TO THE 
LABORATORY SAMPLES OF MATERIALS IN USE IN CON- 
STRUCTING ASPHALT PAVEMENTS. 

In order that a laboratory examination, which has already been 
shown to be necessary, may be satisfactorily carried out the samples 
which are collected for this purpose should be carefully taken and 
according to some system. 

The following directions have been prepared by the author for 
the use of superintendents and yard foremen. 

The materials for the construction of asphalt pavements 
which require inspection in the laboratory may be classified as 
follows : 
In Use in Foundation. 

Broken stone, gravel, sand, hydraulic cement. 
In Use in Binder. 

Broken stone, bituminous cement. 
[n Use in Surface. 

Stone for asphaltic concrete, sand, dust, or filler, refined asphalt, 
fluxing agents, either eastern residuum, California asphaltic 
oil, or other similar substances, and prepared from these 
materials, asphalt cement and the surface mixture itself. 

509 



510 THE MODERN ASPHALT PAVEMENT. 

These materials should be of satisfactory quality, and in order 
to determine this, samples should be sent for examination and 
report to the New York Testing Laboratory, Maurer, N. J. Fol- 
lowing are directions, which must be closely observed, for collect- 
ing and forwarding these samples from every city where contracts 
are made and under way. 

Samples and Specimens. — § 1. To begin with, it must be 
explained that there is a decided difference between a sample 
and a specimen of any material. A specimen is some of the mate- 
rial selected to show its prominent characteristics, either of an 
inferior or desirable nature. A sample, if properly taken, represents 
the average composition and character of the material it represents. 

Specimens are preferable to samples in certain instances and 
the reverse. When it is desired to emphasize the peculiarities of 
some material, a specimen is needed; but when a quantitative 
determination of its characteristics is to be made, a sample is 
necessary. 

This distinction must be borne in mind in sending materials 
to the laboratory for examination, and good judgment must be 
used in regard to the most satisfactory means of arriving at the 
desired end. 

Materials for Foundation. — § 2. No samples of broken stone, 
sand, or cement need be forwarded, unless there is some question as 
to their suitability or quality, or unless they fail to meet the approval 
of the local engineers. Under the latter circumstance, two or 
three fragments of broken stone, a small sample box of sand, or 
four pounds of hydraulic cement should be sent to the laboratory, 
carefully identified as to the source from which the material comes 
and as to the parties furnishing the same. 

Materials for Binder. — § 3. No samples of broken stone or gravel 
for binder need be forwarded unless their quality be in question. 
Samples of asphalt cement for binder should be sent in the same 
way as those for surface mixture, if especially made for binder. 

Materials for Surface Mixture. — § 4. Sand. — In the case of 
sand supplies which have not been previously in use, and in every 
case at the beginning of a new season's work, samples of the one 



SAMPLES OF MATERIALS FOR THE LABORATORY. 511 

or more sands the use of which is proposed, or information in 
regard to the nature of which is desired, should be sent to the 
laboratory with definite statements as to source, whether river, 
lake, bank, etc., with the name of the party furnishing it and the 
locality in which the sand is found. These samples should weigh 
from two to three pounds, as much as will fill a cigar-box holding 
fifty cigars. The sample should be moistened and tightly packed 
so that the finer sand particles cannot sift out and be lost. 

Samples of sand supplies which have been approved need 
not be sent again during the same season, unless the character 
of the deliveries appears to have changed decidedly or is sus- 
pected to have done so. 

Samples of the sand in use on the platform, after it has been 
heated and screened should be sent to the laboratory once a week, 
when the plant is running. The quantity contained in the ordinary 
screw-top tin sample box is sufficient in this case unless other- 
wise directed. 

§ 5. Dust and Filler. — The ground mineral matter, or dust, 
proposed for use as a filler should be sent in whenever a new 
source of supply is contemplated, and its use not begun until its 
quality has been approved. 

From each delivery of such material a sample should be for- 
warded for examination. 

The amount contained in an ordinary tin sample box is, in 
either case, sufficient for this purpose. 

§ 6. Refined Asphalt. — Of refined Trinidad or Bermudez 
asphalt it is unnecessary to send samples from the paving plants, 
as this material has usually been inspected at the refineries. If, 
however, a shipment or any part of it appears to be of inferior 
quality or dirty, a convenient sized specimen, showing the defects 
noticed, should be provided for examination. 

Asphalt from any other source which may happen to be in 
use, either experimentally or otherwise, should be sent in for 
examination in the form of a convenient sized representative 
specimen. 

§ 7. Fluxing Agents. — A sample of each shipment or tank 
car of residuum, California soft asphalt or similar material in use 



512 THE MODERN ASPHALT PAVEMENT. 

for softening the hardei asphalts in making asphalt cement, 
should be sent in a tin can by express, not less than a pint in 
amount. 

Materials similar to blown oils can be sent in a box. 

§ 8. Asphalt Cements. — Samples of asphalt cements from. 
every tank that is put in use should be taken at that time and for- 
warded to the laboratory. If the consistency of that tank of 
cement becomes altered at any time during the day by the addi- 
tion of oil or flux, a new sample should be taken. 

If the asphalt cement in any tank is not exhausted in one 
day's run, and is in use again one or more days afterwards, samples 
for each of these days should be taken and sent to the laboratory, 
stating at the same time on a postal card, giving the number of 
the sample, the amount of oil or flux that has been added per every 
hundred pounds of cement estimated to be in the tank or dipping- 
tank at the time the oil was added. The screw-top tin sample 
boxes are to be used for this purpose. 

§ 9. Surface Mixture. — Samples of surface mixture should 
be forwarded daily. For ordinary work one is sufficient, but 
where an important piece of work, subject to trying conditions, 
is completed in one day, two or three samples, taken at intervals 
while the mixture is being sent out, should be sent, to better illustrate 
the average composition of the surface. 

Sampling Methods to be Employed. — § 10. Unless the sampling 
of any material that is to be examined is carefully done, the sample 
will not be a representative one, and all work done upon it will be 
wasted. The results will be worse than useless — that is to say, 
deceiving. Too much emphasis cannot be placed, therefore, on 
the necessity for great care in this direction. In addition to 
what has already been said in regard to sending samples to the 
laboratory, the following suggestions for taking them should be 
followed closely. 

§11. Sampling Sand: 

1st. From Pit or Bank. — It must be borne in mind that in a 
pit or bank the sand lies in layers of different grading, which can 
almost never be taken out separately. Experience has shown 
that the best that can be done is to obtain a supply representing 



SAMPLES OF MATERIALS FOR THE LABORATORY. 513 

the average composition of the face of the bank. It is useless, 
therefore, to send specimens of sand from strata that cannot be 
isolated; or, if they are sent, specimens of the other layers in the 
bank should accompany them, with a statement of their relative 
thickness. A proper sample can be obtained by cutting a groove 
down the face of the bank and collecting the material in a pile 
and sampling as described below. 

2d. From Rivers or Lakeshores. — In case it is desired to sample 
sands from river bottoms or lakeshores, it is impossible in ordinary 
cases to send in more than what is considered to be a representative 
specimen of the material, and final sampling must await deliveries 
on scow or car. 

3d. Deliveries of Sand should be sampled as follows: Small 
scoopfuls or shovelfuls are taken from different parts of the pile, 
car, or boat load, and at different depths, in such number as will 
fairly represent the lot, three to six, from a canal-boat or barge 
and at depths of a foot or more, two from a car, and more or less 
from a pile, depending on its size. When the sand is in a pile 
the coarser grains will have rolled to the bottom, so care must be 
exercised not to take the sand from that point or the top alone. It 
is also well to dig some distance into the heap for some scoop- 
fuls. 

All the sand thus collected is dried, and, if large in amount, 
is made into a heap, cut back and forth with shovels like a batch 
of concrete and quartered, all but one quarter being rejected. 
This is continued until the heap is reduced to such a size that it 
can be passed through a Clarkson sampler, found at some of the 
works, or sampled by rolling first in one direction and then at 
right angles on brown paper and halving the mass, this being done 
several times until it is reduced to the required size for shipping. 

4th. Sand from Platform. — Samples of the hot screened sand 
in use in the mixer should be taken from the spout of the sand- 
bin while the sand is running out freely into the box in the 
process of filling it. It should be collected by running a shovel or 
scoop back and forth several times along the edge of the distribu- 
tor and then sampling the lot so gathered, either in a Clarkson 
sampler or by rolling on paper in the usual way. 



514 THE MODERN ASPHALT PAVEMENT. 

Where there is no sand-bin a sample may be taken from the 
floor pile, as already described from a delivery pile. 

§ 12. For sampling material of larger size, such as a barrel 
of refined Trinidad asphalt, it should be broken up on a tarpaulin 
and reduced to a size so fine that it can be treated in the same 
way as sand. Usually, as has been said, specimens only of rock, 
gravel, refined asphalt, and such materials are sufficient. 

§ 13. Sampling Asphalt Cement. — It is difficult to always 
obtain uniform samples of asphalt cement. From the same 
bucket samples have been taken which varied as much as six 
points in penetration, owing to imperfections in the way it was 
dipped, a dirty bucket, or lack of uniformity in the cement. Great 
care should be used, therefore, to see that none of the conditions 
surrounding the dipping is abnormal. The dipping-bucket should 
be immersed in the cement until it is of the same temperature, 
and should then be moved about rapidly and submerged upside 
down and full of air to the middle depth of the still and then 
turned over, filled, withdrawn, and the tin sample boxes filled 
where dust cannot reach them. 

§ 14. Sampling Surface Mixture. — A small wooden paddle 
with a blade 3 to 4 inches wide, 5 or 6 inches long, and J an inch 
thick, tapered to an edge at one end and with a convenient handle 
at the other, is used to take as much of the hot mixture from the 
wagon as it will hold, being careful to avoid any of the last drop- 
pings from the mixer which may not be entirely representative 
of the average mixture. Samples of mixture should never be 
taken from the mixer itself, but only from the wagon after mixing 
is completed. 

In the meantime a piece of brown manilla paper with a fairly 
smooth surface, 10 or 12 inches wide, and torn off at the same 
length from a roll of this paper, which can be had at any paper 
warehouse, is creased down the middle and opened out on some 
very firm and smooth surface of wood, not stone or metal, which 
would conduct heat too rapidly. The hot mixture is dropped 
into the paper sideways from the paddle and half of the paper 
doubled over on it. The mixture is then pressed down flat with 
a block of wood of convenient size until the surface is flat. It 



SAMPLES OF MATERIALS FOR THE LABORATORY. 515 

is then struck five or six sharp blows with the block, until the 
pat is about a J inch thick. The paper should then be opened 
and the pat trimmed with an ordinary table knife or spatula to a 
size of about 2\ by 4 inches, and a crease made along the narrower 
edge at a distance of \ an inch to facilitate breaking off a piece 
for analysis when the pat is cold. Before the mixture is entirely 
cold the proportions of sand, dust, and asphalt cement, together 
with the sample number, date, and abbreviation of the name 
of the city where the sample is taken, is impressed upon it with 
steel stamps in letters and figures J of an inch high. The paper 
is also marked with a rubber stamp, identifying it with the pat. 
Additional information as to street, kind of dust, asphalt, 
etc., can also be provided for in blank spaces opposite headings 
printed by the rubber stamp. Such a stamp may be arranged 
as follows: 

Name of city 

Sample number 

Date and hour 

Street 

Sand, coarse 

Sand, medium 

Sand, fine 

Filler, kind 

A. C 

Asphalt, source 

Flux, kind 

Penetration A. C 

Temperature 

The pat papers should be wrapped about the pat when cold 
and both placed in a heavy clasp envelope for mailing at fourth- 
class rates. 

The pat paper is sent because the stain made upon it by the 
asphalt of the hot mixture, when considered in connection with 
the temperature of the mixture as it goes on the street, is of great 
value in determining whether a suitable amount of bitumen is 
present. Nothing should be written on the pat paper, as this 
renders the entire pat liable to letter rates in mailing, but the 
information required may be sent by filling in the blanks furnished 



516 THE MODERN ASPHALT PAVEMENT. 

by the rubber stamp on a postal card and mailing this at the 
same time. 

§ 15. Samples of Old Asphalt Surfaces. — Where the determina- 
tion of the characteristics of an old asphalt surface is desired a 
piece of the surface, together with the adhering binder course, 
if one has been used, is selected which will represent the average 
condition of the street. This should weigh at least 1 pound, and 
it is generally desirable that two or more samples from each street 
should be taken. 

Collecting Samples.— § 16. Samples of stone, cement, sand, 
refined asphalt, flux, etc., can be taken by any one about the 
plant who is competent to follow the directions which have been 
given but samples of mixture and asphalt cement should be taken 
by the plant foreman himself and by no other person. When 
there is a sub-laboratory at a paving plant the chemist in charge 
will have general supervision, and may, if requested by the plant 
foreman, attend to the collection of samples. The plant foreman 
will be held responsible in all cases, through the local superin- 
tendent, for the representative nature of the samples or speci- 
mens which are forwarded to the laboratory and for any deviation 
from the preceding instructions. It is especially urged upon the 
superintendents that they shall see that these instructions are 
carried out, and it is suggested that, to fully benefit by the results 
of the laboratory examinations, samples should be sent not only 
of the best but of the poorest work at each plant, in the latter 
case calling attention to that fact and giving the cause of the 
defect. 

It is recommended that superintendents require their plant 
foremen to initial all reports from the laboratory in order that it 
may appear that the information given there has been brought to 
their attention. 

Samples of asphalt cement and surface mixture should usually 
be taken as soon, after starting up the plant, as the work is going 
on regularly. The dipping-tank may be sampled at once so as 
to be able to mail it, as soon as cool, at an early hour. Any change 
in the character of the cement or addition to it demands a new 
sample, coupled with details of the change. If a second lot of 



SAMPLES OF MATERIALS FOR THE LABORATORY. 517 

cement goes into use later in the same day this should also be 
sampled immediately and sent to the laboratory as soon as possible. 

A second sample of mixture should be taken if any decided 
change in it is made, such as increasing or decreasing the amount 
of asphalt cement, dust, or proportions of different sands. 

The capacity of. the laboratory for work is large, and if the 
rejection of any sample is necessary it is better done according 
to judgment exercised there than at the works. 

Numbering and Mailing Samples. — § 17. The samples of 
residuum, sand, and dust should be numbered consecutively, 
regardless of each other and of all other samples. For instance, 
the first sample of residuum sent for analysis would be No. 1, the 
second sample No. 2, and so on. The same would be true of the 
sand and dust, the first sample of each of these materials being 
No. 1 and the second No. 2, etc. 

Samples of surface mixture will be. numbered consecutively, 
but in case two samples of asphalt cement and only one of sur- 
face mixture are sent on the same day, the number of the second 
sample of asphalt cement should be the same as the first, but a 
figure " 2 " should be placed slightly above the right-hand upper 
corner and a " 3 " for a third corresponding to the same sample 
of surface. For instance, supposing that only one sample of 
surface mixture, No. 10, is sent on one day, but two of asphalt 
cement, the latter would be numbered 10 and 10 2 . In this way 
the A. C. sample number will be made to agree with that of the 
surface mixture in which it was used. If two samples of surface 
mixture and two of asphalt cement are sent on the same day 
the numbers on each should correspond. 

It must be insisted upon that too much care cannot be taken 
to so thoroughly identify samples that there may be no difficulty 
in recognizing their origin and source, even after the lapse of 
years. The habit of sending materials with a designation by 
number, or otherwise known only to the local superintendent, 
must be discontinued. 

Samples from the plant should be mailed at once, or, if hot, 
as soon as cool, and usually at or about noon of the day on which 
the material represented by the samples is used. It may, of 



518 THE MODERN ASPHALT PAVEMENT. 

course, be necessary to mail others in the afternoon, but morn- 
ing samples should in all cases be sent promptly and from the 
nearest letter-box to the works. The practice of sending samples 
to the superintendent's office should be discontinued. Duplicate 
samples can be sent to him for his inspection if he desires. 

In order to check delays in the mails and in other ways it 
is well to mark the date and time of mailing on each package, and 
it should be made the special duty of some one person to attend 
to this matter, and he should be held responsible for mailing. 

A new series of sample numbers for each material or class of 
materials should be started on January 1 of each year. 



CHAPTER XXVIII. 

METHODS EMPLOYED IN THE ASPHALT-PAVING INDUSTRY 
FOR THE CHEMICAL AND PHYSICAL EXAMINATION OF 
THE MATERIALS OF CONSTRUCTION. 

The results of the examination of the materials in use in the 
construction of asphalt pavements will be of no value unless the 
samples or specimens representing these materials are collected 
with great care, so that they shall be truly representative of 
whatever is to be examined The directions given in the preceding 
chapter should, therefore, be followed in taking them. 

The methods practised in the asphalt-paving industry in judging 
the different materials are as follows. It may be said in the begin- 
ning that these methods make no claim to great analytical accuracy, 
but afford that information needed in the industry with a maximum 
amount of accuracy and rapidity at a minimum expenditure of 
time. Many of them are only of relative value; that is to say, they 
do not furnish absolute data and can only be used when some well- 
known specimen of the same material is treated in a parallel 
manner and used as a standard of comparison, as will appear later. 

Stone, Gravel, Slag, etc. — These materials, which form the coarser 
part of the aggregate in the foundation and the entire aggregate 
of the binder, can generally be examined by the hand-and-eye 
method without submitting them to laboratory tests. They should 
be free from adventitious matter, soil, vegetable debris, etc. They 
should be hard and when shaken together or passed through heating- 
drums should produce but a small amount of detritus. If necessary 
the percentage of this, formed in a given length of time when a 
definite weight of the material is revolved in a rattler, such as is 
used in testing paving bricks, may be determined. 

519 



520 THE MODERN ASPHALT PAVEMENT. 

For binder, stone should not be too porous and tests for the 
amount of water absorbed in twenty-four hours should be made. 

As a rule the examination of these materials for use in the 
asphalt-paving industry is in no respects different from that which 
would be made were they to be used for other purposes. A more 
elaborate examination of any stone available for road construction 
will be made by the Office of Public Roads, U. S. Department 
of Agriculture, Washington, D. C, on application on forms sup* 
plied by the Department. 

Where it is desirable to determine the proportions of stone of 
different sizes which go to make up the aggregate of crushed rock, 
as in arranging the grading of an asphaltic concrete, this can be 
determined by means of riddles. These consist of perforated 
metal set in circular wooden frames sixteen inches in diameter, 
with circular openings of the following diameter: 

1 inch, | inch, J inch, | inch and \ inch. 

Binder Cement. — This is generally examined for its consistency 
alone by the same method as asphalt cement for surface mixture. 

Sand. — This is examined as to the material of which the grains 
are composed, their shape, the character of their surface, the 
amount of silt, clay, loam, coal, or vegetable debris it contains, 
the size of the grains, or the sand grading as it is called, and the 
voids in the sand when compacted. The grains of sand are more 
often quartz than other minerals. At times some limestone 
grains or shells are present and rarely a considerable portion of the 
grains are silicates of igneous and volcanic origin, feldspar, horn- 
blende, shales, magnetite, etc., as at Siboney beach, in Cuba, and 
in Mexico. At Santiago sands derived from coral reefs occur. 
These different minerals are determined in the usual way by exam- 



METHODS OF ANALYSIS. 521 

ination under the glass and with reagents. The shape of the 
sand grains is important and is noted with a glass. It may be 
classed as sharp, round, medium, irregular, and with greater detail 
as to special peculiarities. The surface of the grains should be 
examined and note made as to whether it is smooth and polished, 
rough like ground glass, or between these grades, and if it is covered 
with any cementing material such as the ferruginous matter adhering 
to the New Jersey sands. The capacity of the surface of the grains 
for adsorbing aqueous vapor may also be determined with the 
object of learning the thickness of the film of asphalt cement 
which it will probably retain. The silt or clay and vegetable 
debris are detected by shaking a volume of 30 cubic centimeters 
of sand with 100 cubic centimeters of water in a graduated 
cylinder until thoroughly wetted and allowing the coarse particles 
to subside. A rough estimate of the amount of silt, etc., may then 
be made by the eye. The separation of sands into grains of various 
sizes by the use of sieves is the most important means of determin- 
ing their availability for paving purposes. Another estimate may 
be reached from the character and amount of material passing the 
finest sieve in use and determining the size of the grains. 

Determination of the Grading of Sands. — This is done with 
a series of sieves consisting of carefully woven brass wire cloth 
stretched upon a tin frame. These cloths were originally so 
selected that the average diameter of the particles which each sieve 
passed bore some definite relation to those passed by the next 
finer sieve. The average diameter of these particles as passed by 
the sieves in 1908 and the names given in the trade to the cloths 
are: 

200-mesh 085 millimeter 

100- " 173 

80- " 231 " 

50- " , .377 " 

40- " 469 " 

30- " 595 " 

20- " 1.002 " 

10- " 2.133 

The 200-mesh cloth was selected as a basis of measurement, 
being the finest available wire cloth, and it was found that the 
average diameter of the largest particles it will pass is .085 mm. 



522 



THE MODERN ASPHALT PAVEMENT. 



It seemed unnecessary to use any cloth, such as the 150-mesh, 
between this and the 100-mesh sieve, as the largest particles passed 
by the latter were only twice the size of those passed by the former. 
For the same reason an 80-mesh sieve was selected for the third 
sieve, as its largest particles were more nearly three times the 
size of those passed by the 200-mesh sieve than any other. A 
50-mesh sieve passing particles about four times as great in diam- 
eter was selected, rejecting the use of the 60. From this point 
the increase in size is greater at each step, as no intermediate sieves 
are available or necessary. The particles passing the 40-, 30-, 
20-, and 10-mesh sieves are approximately six, eight, twelve, and 
twenty-four times the diameter of the finest particles. 

Obtaining satisfactory sieves of this description is not readily 
accomplished. Most of those found in the trade are made of 
poorly woven cloth or the cloth is so stretched in putting it on 
the frames that the interstices between the wires are much altered 
in size and no two sieves of the same number will agree. It is 
only satisfactory, therefore, to use sieves which have been care- 
fully tested and compared among themselves and with a standard 
set, or to determine the factor for correction as recommended by 
Hazen. 1 

Sieves can now be had in such perfection from Howard & Morse, 
1197 DeKalb Avenue, Brooklyn, N. Y., that a sand sifted on 
one set of sieves in Mexico and on another in the New York Test- 
ing Laboratory by different operators agreed remarkably welL 





Mexico. 


New York 

Testing 

Laboratory. 


Passing 200-mesh 


3% 

6 

8 
35 
25 
13 

7 

3 

100 


1% 

5 

7 
35 
28 
12 

8 
4 

100 


' ' 100- ' ' 


" 80- " 


" 50- " 


" 40- ' ' 


" 30- " 


" 20- " 


" 10- " 





1 Report of Mass. State Board of Health, 1892, 541. 



METHODS OF ANALYSIS. 



523 



The finest cloth, in the 200-mesh sieve, is so delicate that it 
must be used with care and continually watched to detect any 
deterioration. Tearing away from the frame is a frequent occur- 
rence, but such a defect or a small hole in the cloth can be stopped 
readily with soft solder, making the sieve as good as new. New 
sieves often have spots of solder in them where defects due to imper- 
fect weaving or strains in mounting the cloth have been stopped 
out. 

The sieves are made in nests, the finest being of the largest 
diameter, about 8 inches, as the greatest area of sifting surface 




HO 120 iSO 140 >60GRAM Q 

SBW75TO«560 55504540.35 3025.20/1510. G Oflg Q 



It 



A 




Fig. 30.— Sand Scale. 

is needed with this cloth. The diameter decreases until that 
of the 10-mesh sieve is only 5 inches. For storage and shipment 
the sieves thus occupy a small space. 

With such a set of sieves the size and grading of the particles 
of a sand can be satisfactorily determined and intelligently expressed. 
The operation of sifting and weighing is conducted as follows: A 
definite weight of sand, 50 grams, is taken. This is weighed out 
on a scoop and beam-scale especially constructed for use in making 
sand sif tings and sensible to half a gram, Fig. 30. It is the ordi- 
nary No. 485 Fairbank's scale, 1 supplied to seedmen for deter- 



Fairbanks Co., New York. 



524 THE MODERN ASPHALT PAVEMENT. 

mining the dust and dirt in flaxseed, modified to weigh a normal 
weight of 50 grams instead of 1 pound. The 50 grams are 
divided by graduations on the beam of this balance into 100 parts 
representing per cents, thus doing away with any calculations. 

The sand thus weighed out is thrown upon the 200-mesh sieve. 
It is important, however, before sifting is begun that the cloth 
of all the screens, and especially the three finest, be thoroughly 
cleaned with a stiff bristle brush from all particles which may 
have become fixed in the meshes. For this purpose a small stiff 
stencil brush, or one that is found in house-furnishing stores 
for scrubbing porous filters, may be used. After rubbing with a 
brush the screen is struck several sharp blows up and down to 
free it from loose particles. 

The knack of using the sieves satisfactorily and quickly can 
hardly be described in print. After some shaking from side to side, 
the sieve is hit sharply on the table or hard surface to dislodge 
particles which have filled the meshes but will not pass through. 
Many attempts have been made to do the sifting by mechani- 
cal shaking devices and with sieves of all sizes at one time, but 
with little success. Where a large number of siftings is required, 
hand work is more reliable and quicker. 

The most satisfactory mechanical device we have found is 
the "Per Se" Tier shaker,* which may be operated by power or 
hand, one of which is in use in the New York Testing Laboratory 
for screening concrete aggregates or when large quantities of 
sand must be considered. 

The sifting is done over a clean piece of paper, and when nothing 
passes the 200-mesh sieve, all lumps of loam or clay which readily 
break up under the fingers having been rubbed to a powder on 
the sieve and the coarser grains cleaned from dust by attrition, the 
residue is returned to the scoop of the balance. 

It will be noticed that some material at this point usually 
remains in the meshes of the wire cloth. This is allowed to remain 
there when the residue is poured from the sieve, and being more 
nearly the size of the grain passed by this sieve than the next 
larger is included with the 200-mesh or the coarser mesh sieves 
with their particular size grains and counted as passing that sieve. 
When the cloth of the sieve is brushed these grains are rejected, 
and, as all the determinations are made by loss and not by direct 
weighing, this is satisfactory. 

* Howard & Morse, Brooklyn, N. Y. 



METHODS OF ANALYSIS. 525 

The per cent of material passing the 200-mesh sieve is arrived 
at as follows: The beam at the point where the poise is put to 
weigh out the original 50 grams of sand is graduated zero, and 
between this point and where the poise balances the empty scoop 
is graduated into 100 parts which may be read as per cents. The 
amount of material which has been passed by the sieve and rejected 
may then be seen at once in per cents on weighing the residue in 
the scoop, and so for subsequent sieves, subtracting of course each 
time the previous reading from the last. 

It may be asked why the 200-mesh sieve is used first and why 
the results are not stated in per cents of materials retained on 
the different sieves, as is commonly the case. One of the reasons 
for using the finest sieve first is that if the dust or fine material 
is not removed at once much of it is blown away and lost in the 
process of sifting. As in this method the percentages are deter- 
mined by loss, the amount disappearing during the sifting of the 
200-mesh sieve first is of no consequence. Another is that the 
fine material adhering to the coarser grains is more readily separated 
from them by attrition in the finer sieves, and that the presence of 
the coarser sand aids in breaking up lumps and expedites sifting. 
In fact when sifting very fine material like dust or filler it is usual 
to place some coarse gravel not passing a 10-mesh sieve, 
or a few pennies, on the 200-mesh to aid in keeping the fine 
cloth clear and to break up lumps, thus doing the work of the coarser 
particles in sand or mineral aggregates which are entirely absent 
from the filler. The results are stated in per cents passing a 
given sieve rather than that retained, because this results in making 
a uniform statement and not some figures passed and some retained, 
and because it is easier to associate the percentages with definite 
sized particles rather than with sieves which will not pass them. 

After the 200-mesh sieve, the others are used in order, and of 
course more rapidly as they become coarser. The greatest care is, 
of course, necessary with the finest sieve to clean the coarse grains 
and to break up lumps of clay, etc., for which the finger ends are 
most suited, as their pressure can be graduated and no undue force 
exerted upon the cloth or upon the particles which do not readily 
disintegrate. 



526 



THE MODERN ASPHALT PAVEMENT. 



The actual subtractions made in a sifting appear in the follow- 
ing facsimile page of a laboratory record, a rubber stamp being 
a decided convenience for reporting purposes: 



No. 30402 



100.0 



13 
4 



27 
13 



14 



5/ 

27 



30 



77 
57 



88 

77 



11 



95 

88 



100 
95 



No 


. 30402 


Mesh 
No. 


Per Cent. 


Passing. 


Bit. 




200 


4.0 


100 


9.0 


80 


14.0 


50 


30.0 


40 


20.0 


30 


11.0 


20 


7.0 


10 


5.0 


R, 10 




Total. . . 


1C0.0 



Remarks : 



Voids in Sand and Mineral Aggregates. — An important con- 
sideration in connection with a sand or mixture of sands for use in 
asphalt pavements is the percentage of voids which it contains 
on compaction. 



METHODS OF ANALYSIS. 527 

The ordinary methods of determining voids by measuring the 
volume of water that must be added to the compacted mineral 
aggregate to fill them, or pouring the compacted aggregate into a 
measured volume of water in a graduate and noting the increase of 
volume, are not satisfactory, because in the first way it is difficult 
to displace all the air in the voids or to know when it is displaced ; 
in the second, because in light sand and sand mixed with filler a cer- 
tain amount of the fine material is with difficulty persuaded not to 
float or leaves at best a meniscus which cannot be read. 

The ordinary means of attaining ultimate compaction is also 
deficient in accuracy. At air temperatures the grains of any 
sand or dust are surrounded by a film of adsorbed aqueous vapor 
which prevents their packing as closely as possible. To attain 
satisfactory compaction the aggregate must be above the tempera- 
ture of boiling water. It is necessary, therefore, to use hot sand 
in determining the voids in fine materials and the finer the ma- 
terial the more necessary it is. 

The sand aggregate should be heated to about 250° F. in a small 
deep-form iron sand-bath 1 and then compacted in one of the fol- 
lowing ways. 

First Method. — A narrow-necked flask, graduated to 100 c.c, 
is filled with hot sand, the neck taken in one hand and with the 
other hand the body of the flask is struck back and forth from the 
neck to the bottom with a peculiar jarring motion with a wooden 
rod of about f of an inch diameter and 12 inches long, covered 
for 3 inches with a piece of rubber tubing. The jarring settles 
the sand together rapidly in the flask and it is necessary to add 
more from time to time. When jarring ceases to compact the sand 
further it is, after having been brought to a definite volume, emp- 
tied on a balance and weighed. For ordinary purposes this 
weight divided by the weight of an equal volume of quartz, 
will give the actual volume the particles of sand occupy, 
and from the difference between this and the volume of the 
flask the voids are learned. When greater accuracy is re- 
quired the flask with the hot sand must be allowed to cool to 
ordinary temperatures, to allow for contraction of the quartz in 

1 Eimer & Amend, No. 4555, 6-inch. 



528 THE MODERN ASPHALT PAVEMENT. 

volume, and again filled to the mark. The specific gravity of the 
sand grains is ordinarily assumed to be 2.65, but it may vary, and 
the possibility of this can be determined at a glance. When this is 
the case the density must be determined, often in petroleum or 
alcohol when fine sand is present. The apparatus designed by 
D. D. Jackson, which has been described by him in a paper before 
the Society of Chemical Industry in 1904,* and which can be 
obtained from Emil Greiner Co., 45 Cliff Street, New York City, 
has been found to be very convenient for this purpose. 

The advantage of this process is that the flask is filled with sand 
at once and there is no segregation of particles of different sizes, 
especially dust, which sometimes takes place in the next method. 

Second Method. — The hot sand is taken as before, but it is 
put into a graduated 100 c.c. cylinder, 10 c.c. at a time, and com- 
pacted by tamping on a block of wood after each addition. When 
the compaction has reached its ultimate limit, this is known by 
a disappearance, especially with fine material, of a noise due to 
the presence of an air-cushion between the particles before this 
point is reached. Segregation takes place to a limited extent, 
especially in mixtures of sand and dust, but even with this error 
a greater compaction and density is obtained and less voids are 
found than with the flask method for the same aggregate, the 
difference being about 1 per cent in favor of the cylinder. 

Volume Weight of Sand. — From the weight in grams of 100 
c.c. of a sand or aggregate, obtained in the determination of the 
voids as just described, the weight per cubic foot in pounds can be 
found by multiplying by the factor .624. This is of value in deter- 
mining what difference in the weight per cent of bitumen to expect 
from the addition of the same volume of asphalt cement to sands 
of different volume weight. 

For example, an aggregate from a western city in 1899 weighed 
124.5 pounds per cubic foot, from another 115.7. It is very easily 
seen that, with the same volume or weight of asphalt cement, 
added to each, the percentage by weight in an ordinary mixture 
will be much lower in the first than in the second city, and in 

* J. Soc. Chem. Ind. 24, 593. 



METHODS OF ANALYSIS. 529 

practice it is found that in one case it was 10 per cent, in the other 
11.3 per cent. This determination of volume weight therefore 
serves as an aid to our interpretation of our gravimetric analysis. 

Dust or Filler. — A dust or filler of ideal quality should consist 
of particles, all of which should be so fine that they will pass a 
200-mesh screen. Everything coarser merely acts as sand. It 
is important, too, that the particles should be much finer than 
a size that will merely pass this sieve. They should be impal- 
pably fine. 200-mesh sand is not the same as dust and is, in fact, 
often undesirable in a surface mixture. 

In examining a dust or filler, therefore, it is necessary to deter- 
mine with the 200-mesh sieve the percentage passing it and to 
study the character of that which passes. The latter examination 
can be made in two ways. As we have no sieve available for the 
purpose it must be done with a microscope or powerful lens which 
will show the character of the grains, or by elutriation. 

Elutriation Method. — Until recently the only means of deter- 
mining the fineness of a dust or filler has been by means of a 
200-mesh sieve, but as the material passing this sieve might con- 
sist in whole or in part of grains as large as .10 mm. in diameter 
which can hardly be considered as dust, but are, on the contrary, 
only fine sand, something more satisfactory is demanded. This 
has been found in the elutriation process in use in soil analysis. 
Five grams of the dust to be examined are placed in a beaker 
about 120 mm. high, holding about 600 c.c. The beaker is nearly 
filled with distilled water, at a temperature of 68° F., and agitated 
with an air-blast until the dust and water are thoroughly mixed. 
On stopping the blast the liquid is allowed to stand exactly 15 
seconds and the water above the sediment immediately decanted 
without pouring off any of the latter. This washing is repeated 
twice. The sediment is washed out into a dish, dried, and weighed. 
The loss in weight represents what may be considered as dust free 
from sand. The washing must be done with distilled water, since 
water containing salts in solution, as is well known, induces floc- 
culation. This method can also be used with hydraulic cements, 
since the material acted upon by water is retained in suspension 
and removed, while that which subsides is practically unacted 



530 THE MODERN ASPHALT PAVEMENT. 

upon and can be dried and weighed without difficulty. The 
differentiation in this case can, however, not be carried beyond 
that resulting in 15 seconds. With other materials the differ- 
entiation of the particles not subsiding in 15 seconds can be carried 
further, if desired, by reagitating the decanted material and allow- 
ing the sedimentation to go on for 1 minute, 30 minutes, 1 hour, 
and so on. The preceding method is an adaptation of that pro- 
posed by Osborne for the separation of the particles of soil of 
various sizes, for further details of which reference must be made 
to the Connecticut Agricultural Station Annual Report, 1886, 
page 141, " Principles and Practice of Agricultural Analysis, 
Wiley, Vol. 1, page 196, and Hazen, 24th Annual Report Mass. 
State Board of Health, 1892, page 543. 

Crude Hard Asphalts. — The analysis of crude asphalt is con- 
ducted in much the same way as that of the refined product except 
that it is necessary to determine, in the former, the loss of water 
and light oil, which are not or should not be found in the refined 
material. If there is any question as to the dryness of the refined 
material this should, of course, be first determined in the same 
manner as with the crude. The determination of water can be 
made in two ways. 

Ordinary Method. — Ordinarily it is sufficiently accurate to 
weigh out 2 to 5 grams of the material in a crucible, or preferably 
on a watch glass to expose more surface, and to subject it to a 
temperature of 100° C, in a well regulated air-bath with the pre- 
cautions described on pp. 534, 535, until it ceases to lose in weight to 
an extent of more than .2 to .3 per cent on successive heating. 
A greater concordance is not sought, as many asphalts continue to 
lose light oils gradually at this temperature. The oven which 
is used for this purpose in the author's laboratory is one of the 
Lothar-Meyer form, or a modification of this, which is fully described 
on page 536, Figs. 31 and 32. The degree of fineness to which the 
crude asphalt should be reduced before weighing out is dependent 
upon the amount of water it contains. In powdering some asphalt, 
such as crude Trinidad, the material, since it contains 29 per cent 
of water in emulsion with bitumen, begins to lose water at once. 
It can, therefore, only be broken into coarse lumps and not reduced 



METHODS OF ANALYSIS. 531 

to a powder until after a preliminary determination of the water 
thus lost by the coarse material. Other asphalts, containing only 
a small amount of hygroscopic or adventitious water, may be 
ground up at once, while some which are not readily powdered 
may be cut into small pieces. If it is necessary to determine the 
water absolutely it may be absorbed and weighed and the difference 
stated as gas or light hydrocarbons. This is hardly necessary from 
a technical point of view. 

"Alternate Method. — For asphalts such as crude Trinidad, in 
which the difficulties described above are met, a different method 
of procedure is advisable. The substance is very quickly reduced 
to a coarse powder only, in a mortar provided with a cover, through 
which the pestle passes. Five grams of it are spread out on a 
4-inch watch-glass, and this is placed in vacuo over sulphuric 
acid for twelve hours and the loss determined. It should then 
be reground to a fine powder and exposed again in vacuo until 
it ceases to lose weight. The loss may be stated as water. 

In the examination of a cargo of crude Trinidad for technical 
purposes, about 50 grams in small lumps are placed in a flat 8-oz. 
oblong tin box and dried to practically constant weight at 325° F. 
The results thus obtained are comparable with those obtained 
in the refining by steam at this temperature. 

In whichever way the asphalt is dried a sufficient quantity is 
prepared and preserved in this condition in a tightly stoppered 
bottle, for analysis. Asphalts which cannot be reduced to powder 
are used in mass. The powdered asphalts have a slight tendency 
to absorb hygroscopic moisture and must be protected from the 
air. 

In the dried condition crude asphalts can be considered, as 
far as analysis is concerned, simply as refined material, and all 
determinations should be done with and percentages calculated to 
this material, including the water or loss, by calculation, in the 
final results if desired. 

Refined Asphalts. — Examination of refined asphalts in their 
most extended form include determinations given on the accompany- 
ing form, used as a convenience in reporting. With well-known 
asphalts but a limited number of determinations are necessary for 



532 THE MODERN ASPHALT PAVEMENT. 

the purpose of detecting the lack of uniformity or peculiarities in 
the material. 

NEW YORK TESTING LABORATORY. 

Test number Maurer, N J 

Source of supply 



Physical Properties. 
Specific gravity, 78° F./78° F. original substance, dry. 

" " pure bitumen 

Color of powder or streak 

Lustre 

Structure 

Fracture. 

Hardness, original substance 

Odor 

Softens 

Flows. 

Penetration at 78° F 



Chemical Characteristics. 
Original substance: 

Loss, 212° F., 1 hour 

Dry substance: 

Loss, 325° F., 7 hours 

Character of residue 

i Penetration of residue at 78° F 

Loss, 400° F., 7 hours (fresh sample) 

Character of residue 

Penetration of residue at 78° F 



Bitumen soluble in CS 2 , air temperature. 

Inorganic or mineral matter 

Difference 



Malthenes : 

Bitumen soluble in 88° naphtha, air temperature.. . . 

This is per cent of total bitumen 

Per cent of soluble bitumen removed by H 2 S0 4 

Per cent of total bitumen as saturated hydrocarbons. 



Bitumen soluble in 62° naphtha. 
This is per cent of total bitumen. 



METHODS OF ANALYSIS. 533 

Carbenes: 

Bitumen insoluble in carbon tetrachloride, air temperature. 
Bitumen more soluble in carbon tetrachloride, air tem- 
perature 

Bitumen yields on ignition: 

Fixed carbon 

Sulphur 

Ultimate composition 

Remarks : 

Physical Properties. — Specific Gravity. — The specific gravity 
of the dried asphalt is taken in a picnometer at 25° C. and referred 
to water at the same temperature. This temperature has been 
selected as the most convenient mean between the room tem- 
peratures of winter and summer, and is much more suitable in 
our surroundings than the lower temperature generally in use 
abroad, 15° C. Determinations at the latter temperature are 
much hampered by the great difference between it and our labora- 
tory temperatures, the rapid expansion after cooling to 15° C. 
being difficult to provide for, as w T ell as the condensation of mois- 
ture on the surface of the picnometer when the dew point is high, 
a room with the temperature in use for penetrations is always 
available for density and other temperature work. This tem- 
perature of 78° F. has therefore been taken as a normal one for 
all physical work on asphalts. The specific gravity of the pure 
bitumen extracted from those asphalts carrying a considerable 
amount of mineral matter, in a way to be subsequently described, 
is also determined in the same way. 

The usual determination of the outward physical features of 
any mineral substance, Color of Streak, Structure, Fracture, Hard- 
ness, and Odor if any, are noted. 

The color of the streak or of the powder of a hard asphalt is 
in certain cases characteristic. For example, in the case of refined 
Trinidad lake asphalt the powder is a bluish-black color, while 
that of the refined Trinidad land asphalt is much browner. Pow- 



534 THE MODERN ASPHALT PAVEMENT. 

dered gilsonite is of a very light-brown color. Powdered gra- 
hamite is quite black. 

The structure of a solid native bitumen may be either homo- 
geneous or it may show the presence of cavities containing gas, 
particles of adventitious mineral matter, shale or clay, or other 
peculiarities. 

The fracture may be, in the case of very pure bitumens, con- 
choidal or semi-conchoidal, pencillated or hackley in the case of 
grahamite, or irregular. 

The hardness of the original material, if it contains much 
mineral matter, may be stated in degrees of Mohrs scale, that 
of the pure bitumen in several ways. It is either brittle, like 
glance pitch, or soft enough to be penetrated with the needle of 
a penetration machine in which case the hardness is expressed 
in degrees of this machine. 

The odor in the case of many bitumens is characteristic. That 
from Venezuelan asphalt, found near the Gulf of Maracaibo, is 
extremely strong and rank, while others are more purely asphaltic, 
especially on warming. The heat in any case brings out the 
odor to a degree not observed in the cold material. 

Loss on Heating. — It is sometimes necessary to determine 
the loss which an asphalt suffers on heating for a time to definite 
temperatures. The length of time has been arbitrarily taken 
as seven hours and the temperature 325° F. and 400° F. 

The determination is made as follows: In a No. 1 crystallizing- 
dish, 2\ inches in diameter and lfV inches high, or 3 oz. deep seam- 
less tin box of this size, 1 are placed 20 grams of the material 
under examination. The exact dimensions of the dish are of no 
great importance, as can be seen from the following determina- 
tions: 

< 

1 American Can Co., New York. 



METHODS OF ANALYSIS 



535 



TWENTY GRAMS OF RESIDUUM AT 325° F. FOR SEVEN HOURS. 



Dish number 

Weight of dish 

Height of dish, outside. 
Diameter of dish, inside 

Thickness of glass 

Volatile per cent 

Position in bath 



23.3465 
1.51" 

2.15" 
.06 
.925 

Left 



18.1825 

1.47" 

2.15" 

.045 

.920 

Right 



19.1855 

1 . 28" 

2.20" 

.05 

.950 

Middle 



Should it be necessary to use a very much larger dish the 
weight of the material to be taken should be calculated so that 
the volume which it holds shall bear the same relation to the 
surface exposed as in the case of the smaller dish. It is necessary 
to take separate portions of the substance for each determination, 
and not to attempt to determine the loss at 400° F. from the 
sample which has been previously heated at 325° F. 

The dish is heated to the requisite temperature for the given 
length of time in an oven the temperature of which is uniform in 
all parts, something that is not as easily accomplished as might 
be supposed, and with the assurance that the materials are main- 
tained at the proper temperature, a temperature which it has 
been found is not indicated by that recorded by a thermometer, 
that registers merely the temperature of the air in the bath. Such 
an oven is not only difficult to obtain, but the manner in which 
the best form is used is of great importance. 

Form of Oven Employed in the Author's Laboratory. — Extended 
experience with various ovens thoroughly convinced the author 
that none of the forms ordinarily furnished by the supply dealers 
were satisfactory, especially if they are heated by the direct appli- 
cation of the flame to the bottom of the oven. The air-bath of 
Lothar-Meyer l was found to be by far the best, but inconvenient, 



1 Berichte, 1889, 22, 1, 879. 



536 



THE MODERN ASPHALT PAVEMENT. 



owing to the fact that the interior is not readily reached. On this 
account an oven has been designed, possessing all the advantages 
of Meyer's form, but much more convenient for use in an asphalt 
laboratory. The accompanying illustrations show its censtruc- 
tion, Figs. 31 and 32. 




Fig. 31. — New York Testing Laboratory Oven. 



It will be seen that the bath instead of being heated from the 
bottom is heated by a 10-inch ring burner immediately under- 
neath the space between the oven itself and the outside wall, as 
in the Lothar-Meyer form. The perforations in this ring are neces- 
sarily systematically spaced to allow for the greater gas pressure at 



METHODS OF ANALYSIS. 537 

the point where the latter enters, in order that a uniform amount of 



»i n n n 




a^ 



Fig. 32. — New York Testing Laboratory Oven. 

heat may be furnished at all points in the circumference. If this 
is properly arranged, and the inner chamber of the bath is well 
made, no further precautions are necessary to avoid inequalities of 
temperature caused by the direct entrance of hot air from the burner 
into the oven. In standardizing the bath it is necessary that a 
number of thermometers should be inserted at different points in 
order to determine that the temperature at all points is uniform. 
If this is not the case the openings in the ring burner must be 
rearranged until this is accomplished. The interior of the bath, it 
will be noticed, is provided with a fan for causing a circulation of 
air to bring about still greater uniformity, this fan being moved by 
any convenient source of power. 

The inner chamber is provided with a perforated shelf of metal. 
The dishes containing the material to be subjected to the desired 
temperature, it has been found, cannot be placed directly on this 



538 THE MODERN ASPHALT PAVEMENT. 

shelf with the assumption that they will not exceed the tempera- 
ture recorded by the thermometers in the air circulating in the 
bath. The conductivity of the metal shelf is so much greater than 
that of the air that the dishes will attain a much higher temperature 
than the air in the bath. This difficulty can be avoided to a very 
considerable extent by placing a sheet of asbestos over the shelf; 
but even then the temperature of the material in the dish will be 
somewhat different from that of the air in the bath. In order to de- 
termine what the temperature of the former is it has been found nec- 
essary to use a thermometer, which is immersed in heavy residuum 
oil placed alongside the material under examination. The reading 
of this thermometer will give the temperature to which the material 
under examination is being subjected. The thermometer exposed 
only to the air of the bath is then observed merely for the purpose 
of detecting any sudden changes. 

It will be noted that the cover to this bath is hinged so that it 
may be opened conveniently for inserting and removing the dishes 
containing the material under examination. It is provided with 
numerous openings for the insertion of thermometers and a gas 
regulator, and for the escape of the vapor of hydrocarbons which 
have been volatilized. The outer shell of the bath is covered 
with asbestos for insulating purposes. 1 

Melting or Flowing Point. — The solid native bitumens can 
have no definite melting point, for the reason that they are com- 
posed of mixtures of hydrocarbons. It is only possible, therefore, 
to determine rather arbitrarily the point at which the material 
softens or flows, and with special reference to the relation of this 
point toward some standard bitumen. This is determined as 
follows: 

A crystallizing dish, about 2\ inches in diameter and with 1% 
inch sides, filled with clean mercury to a distance of J inch from 
the top, is placed over a 20-mesh wire gauze and heated by a 
small flame protected from draughts by a chimney. On the sur- 
face of the mercury is placed a thin microscopic cover-glass, 
No. 2-0, carrying the specimen of asphalt under examination. 

x The bath is constructed for the author by the Hauck-Seebach Co., 291 
Essex Street, Brooklyn, N. Y. 



METHODS OF ANALYSIS. 



539 



When dealing with hard asphalts that can be ground rather 
coarsely, several fragments which will pass a 40-mesh sieve and 
be retained on a 50-mesh sieve (about .50 mm. diameter) are 
spread on the cover glass and placed upon the surface of the 



• ' .." _. ■ ' 1' : :j 



Fig. 33 



mercury, covered with a funnel, from which the stem has been 
cut and the thermometer passed through the orifice until the 
bulb is immersed in the mercury. It is held in position by a 
clamp attached to the ring-stand holding the dish. Under the 
dish a burner is placed that can be regulated to a small flame and 



540 THE MODERN ASPHALT PAVEMENT. 

heat, so that the rise of temperature will be from three to five 
degrees per minute. In a short time it will be noticed that the 
specimens will have changed from the brown or brownish-black 
color of the powder to that more nearly approaching the original, 
with a slight rounding of the individual grains. On further heat- 
ing these globules flow together and form a thin sheet on the glass. 
The point at which the specimen begins to flow, as indicated by 
the thermometer, is noted as the melting or flowing point. 

Asphalts that cannot be ground are softened and pulled out 
to a thread and cut into small pieces, about 1 cubic mm. Sev- 
eral pieces should be placed on the glass together, as one will 
serve as a check on the other, and thereby lessen the chance of 
error. The softening point may be noted by the rounding of 
the particles and the beginning of the flow, or when the specimen 
begins to spread out, which is always at the point of contact with 
the cover-glass, is set down as the flowing point or the tempera- 
ture at which the specimen will melt. 

Determination of Total Bitumen. — One gram of the dried 
or refined material, in a state of very fine powder, if possible, is 
weighed out and introduced into a 200 c.c. Erlenmeyer flask of 
Jena glass and covered with about 100 c.c. of bisulphide of carbon. 
It is then set aside for at least five hours, or overnight, at the tem- 
perature of the laboratory. In the meantime a Gooch crucible 
is prepared with an asbestos felt and weighed. This Gooch 
crucible is of special form with a large filtering surface. It holds 
30 c.c, is 4.4 cm. wide at the top, tapering to 3.6 cm. at the 
bottom and 2.6 cm. deep. This is much better for percolation work 
than the usual narrow form of Gooch. The felt is made by beating, 
up long-fibre Italian asbestos in a mortar, and suspending the finei 
particles in water and quickly pouring off from the coarse particles. 
Too much of the latter should not be removed, or the felt will be 
too dense. The decanted asbestos and water can be kept in a 
bottle for use. To prepare the felt the asbestos and water are 
shaken up and what is found to be a proper amount poured into 
the crucible, which has in the meantime been attached to a vacuum 
filtering-flask by the proper glass and rubber connections. As 
soon as the asbestos has somewhat settled the vacuum-pump is 



METHODS OF ANALYSIS. 541 

started and the felt firmly drawn on the bottom of the crucible. 
It is then dried, ignited, and weighed. 

After standing a proper time the bisulphide is decanted very 
carefully upon the filter which is supported in the neck of a wide- 
mouth flask and allowed to run through without pressure. The 
flask after being tipped to pour the first portion is not again placed 
erect in order to avoid stirring up the insoluble material, but is 
held at an angle on any suitable base, such as a clay chimney. 
After all the bisulphide has been decanted more is added and 
the insoluble matter shaken up with it. This is allowed to settle 
and decanted as before, the insoluble matter being finally brought 
on the filter and washed with the solvent until clean. The excess 
of bisulphide is allowed to evaporate from the Gooch crucible 
at the temperature of the room. It is then dried for a short time 
at 100° C. and weighed. The loss of weight is the percentage of 
bitumen soluble in CS2. 

In the meantime, however, the bisulphide which has passed 
the filter is allowed to subside for twenty-four hours, if possible, 
and is then decanted carefully from the flask in which it has been 
received into a weighed platinum or unweighed porcelain dish. 
If there is any sediment in this flask it must be rinsed back into 
the Gooch crucible with bisulphide and the crucible again washed 
clean. The solvent in the dish is placed in a good draught and 
lighted. When all the bisulphide has burned, the bitumen 
remaining in the dish is burned off over a lamp and the mineral 
residue, which was too fine to subside, is weighed, if the burning 
was done in a platinum dish, or dusted out and added to the cru- 
cible if in a porcelain one. In the former case the weight is added 
to that of the Gooch crucible or subtracted from the per cent 
of bitumen, found without its consideration, as a correction. 
Care must be used in this method of procedure that the solvent 
does not creep over the sides of the crucible and that the outside 
is free from bitumen before weighing. In order to avoid this the 
crucible is supported in the neck of a flask with three constrictions, 
the neck extending above the top of the crucible and the latter 
being covered with a watch-glass. These flasks are made for 



542 THE MODERN ASPHALT PAVEMENT. 

the author by E. Machlett & Son ; 143 East Twenty-third Street, 
New York. 

Mineral Matter or Ash. — One gram of the same sample of 
material used fqr the determination of bitumen is weighed out in a 
No. Royal Berlin porcelain crucible and burned in a muffle or 
over a flame until free from carbon. This must be determined 
by breaking up the cake of ash, moistening with water or alcohol, 
and observing if any black particles of coke are present. The 
weight of the residue is stated as inorganic or mineral matter. 

The determination is of course not exact, sulphuric acid and 
the alkalies being volatilized in many cases, but it is satisfactory 
for technical purposes. 

Naphtha Soluble Bitumen. — For the purpose of determining the 
percentage of bitumen soluble in naphtha distillates, 88° and 62° B. 
are used. It is extremely important that these naphthas should be 
of the exact degree specified, since differences in density will make 
an appreciable difference in the amount of bitumen extracted. 
The distillate should be that obtained from a paraffine petroleum. 
The density of each lot should be carefully determined with a 
Westphal balance at 60° F. and if it is too dense or too light, it 
can be brought to the proper density by diluting with a heavier 
or lighter naphtha as required. Redistillation of these naphthas is 
unnecessary as the products of distillation are no more uniform 
than the original naphtha. 

It will be found very necessary that hard bitumens should be 
reduced to an impalpable powder before attempting to extract 
them, as otherwise the extraction will not be complete. The softer 
bitumens should be divided as much as possible. 

The bitumen is usually extracted with naphthas of both densi- 
ties in order to determine the difference in their action. If the 
amount extracted by each is the same or nearly the same it will point 
to the fact that the bitumen consists of hard asphaltenes mixed with 
light malthenes, the latter equally soluble in naphtha of both 
degrees of density, and but little intermediate hydrocarbons, or of 
the very hard asphalts fluxed artificially with some light oil. 
If, on the other hand, there is a very considerable increase in the 
percentage dissolved by the 62° over the 88° naphtha it may be 



METHODS OF ANALYSIS. 



543 



assumed that the malthenes are well graded and natural constitu- 
ents of the bitumen which is being examined. In certain cases, 
however, the use of the two naphthas is unnecessary. It would be 
useless to extract a maltha with a dense naphtha or glance pitch 
or albert ite with a lighter one. 

In determining the naphtha soluble bitumen in asphalts and 
other hydrocarbons it was the custom from 1887 to 1899 to make 
the extractions in small beakers, No. 0. One gram of the substance 
was weighed out and covered with a sufficient amount of naphtha, 
about 75 c.c, and placed on the steam bath and allowed to boil 
until the solvent became thoroughly saturated. It was then 
decanted through a weighed Gooch crucible and the residue succes- 
sively treated until free from bitumen soluble in naphtha. As it 
was almost impossible to get concordant results in this way, on 
account of the loss of the lighter constituents of the naphtha and 
the consequent increase of density of the solvent, resort was had 
to the use of Erlenmeyer flasks, about 12 cm. high and 200 c.c. 
capacity. One gram of the substance was weighed out and boiled 
with the naphtha in a loosely stoppered flask for from one-half 
to one hour, according to the character of the material to be ex- 
tracted. The solution was decanted as with the beaker method 
and the treatment repeated. The results were a slight improve- 
ment over the open beaker, but not entirely satisfactory. The use 
of a return cooler was then tried and gave good results with 62° 
naphtha, but as the loss of light hydrocarbons from the 88° naphtha 
could not be controlled, even in this way, any heating with this 
very volatile solvent was abandoned. The change in the two grades 
of naphtha on heating are shown from the following experiments: 

EFFECT OF HEATING NAPHTHA AS IF USED AS A SOLVENT. 



Degrees B. 


Gravity 
15° C./15° C. 


Treatment. 


Loss by- 
Weight, 
Per Cent. 


Loss by- 
Volume, 
Per Cent. 


Residue, 
Specific 
Gravity. 


88° 
it 

tt 
62° 


. 6379 
. 6379 
. 6379 

. 7321 
0.7321 


Return cooler 
tt it 

Open flask 

Return cooler 
Open flask 


51.2 
65.6 
53.5 

3.0 
10.0 


40.0 
37.0 

48.0 

1.0 
3.0 


0.6523 
0.6523 
0.6585 

0.7352 
0.7393 



544 THE MODERN ASPHALT PAVEMENT. 

It appears, therefore, that heating increases the density of both 
naphthas, and consequently their solvent powers, from inability 
to condense the more volatile parts, but that the change in the 62° 
naphtha is small, so that it can be safely heated to a slight extent. 

As a result of these experiments all determinations are now 
made with cold naphtha by the following method: 

One gram of the substance is weighed into a 200 c.c. Erlenmeyer 
flask, covered with naphtha and allowed to stand, as in estimating 
total bitumen, in fact the entire process is the same with the ex- 
ception that one or two precautions must be observed.' It is well 
not to attempt to break up any lumps with a stirring rod, as the sub- 
stance, especially the softer asphalts, may then adhere to the rod 
or flask and be difficult to detach. It may also be necessary to 
treat the substance with several portions of the solvent instead 
of with two or three, as in the case of carbon disulphide. No heat 
is applied at any time in the process. 

The naphtha soluble bitumens are frequently denominated 
petrolenes. The writer has recently suggested the name malthenes 
as bitumen of this nature closely resembles maltha in its consis- 
tency. Objection has been raised by partisans to the use of the 
name petrolene as leading to the conclusion that petrolene is a defi- 
nite compound. Of course it is no more a definite compound than 
kerosene, but a mixture of various hydrocarbons like the latter. 
The objection to this designation must, therefore, fall to the ground, 
although petrolenes or malthenes may be more satisfactory as being 
less misleading. 

Determination of the Character of the Malthenes or Naphtha 
Soluble Bitumens. — The determination of the relative proportion 
of saturated and unsaturated hydrocarbons which constitute the 
malthenes is very important in differentiating the solid bitumens. 
It is made as follows: 

The 88° naphtha solution of the bitumen under examination 
is made up to a volume of 100 c.c. or reduced to that volume by 
evaporation. It is then placed in a 500-c.c. separatory funnel. 
An equal volume of the solvent naphtha is placed in another sepa- 
ratory funnel. The naphtha solution and the naphtha are then 
subjected to the action of 30 c.c. of sulphuric acid of specific 



METHODS OF ANALYSIS. 545 

gravity 1.84, the acid and the naphtha V>eing shaken together for 
exactly three minutes. This is most important, since the action 
of the acid on the hydrocarbons in the bitumen under examina- 
tion is not a fixed one, but will continue more or less indefinitely. 
After the shaking, the acid and the naphtha solution are allowed 
to stand overnight. The acid is then carefully drawn off and the 
shaking again repeated with another volume of acid of the same 
amount. This will require a shorter time for the separation of the 
acid and it can be drawn off within a few hours. " If the second acid 
is very strongly discolored the acid treatment should be continued 
a third time. In the case of the blank determination with the 
plain solvent one treatment will be sufficient. The naphtha 
solution and the naphtha are then washed twice with water and 
afterwards once with a 5 per cent carbonate of soda solution, 
after which one further washing with water takes place. The 
naphtha solution of the bitumen which is being treated and the 
blank naphtha are then poured into crystallizing dishes 3^ inches 
in diameter and 2 inches deep. In the plain naphtha is dissolved 
from .50 to .75 gram of some extremely stable petroleum residuum. 
The two dishes are then placed upon the steam-bath to evaporate 
the naphtha. In order to avoid creeping, the sides of the dishes 
are imbedded in a mass of cotton waste reaching to the top, as 
creeping is much diminished by having the sides of the dish warm. 
The evaporation is carried on on the steam-bath until the naphtha 
is volatilized and until the blank shows on weighing that the 
residue has returned to its original weight. It is then as- 
sumed that the other dish is free from naphtha, and from 
the water which the latter has dissolved in the process of washing. 
This, under the conditions observed in the author's laboratory, 
will require about six hours, but the exposure on the water-bath 
is generally continued one hour after the blank has reached a 
constant weight and further for fifteen minutes in an air-bath at 
100° C. as control. The results obtained in this way are of no 
absolute value, but are of relative importance in comparing differ- 
ent fluxes and solid bitumens. It cannot, of course, be applied 
where the bitumen contains an appreciable amount of hydro- 
carbons volatile at 100° C. 



546 THE -MODERN ASPHALT PAVEMENT. 

Where 62° naphtha is the solvent its volatilization from the 
residue of bitumen which has been treated is extremely difficult, 
and such a determination is, therefore, not recommended. 

Determination of Bitumen Soluble in Carbon Tetrachloride. — 
While in the large majority of cases the same, or nearly the same, 
amount of bitumen is dissolved by carbon tetrachloride as by bisul- 
phide of carbon, bitumens are known in which hydrocarbons 
exist which are not as soluble in the former solvent — for example, 
one of the Venezuelan asphalts when overheated in refining, 
grahamite, and some of the residual pitches. The use of this 
solvent may, therefore, be desirable at times for the purpose of 
differentiating the native bitumens. The insoluble matter is 
extremely fine and is with difficulty retained on the closest filters. 
It appears to coagulate after several hours and in conducting the 
operation should be allowed to stand over night before filtering. 
A mild current of air passed for an hour through the solution 
accomplishes the same purpose, and may be used to hasten 
the analysis when desired. 

One gram of the sample is treated with 100 cc. of the cold 
solvent, and with the exception of the precautions above noted, 
filtered in exactly the same way as with carbon disulphide. 

The following data are given in illustration of the effect of 
different methods of handling. 

Filtered as soon as dissolved £9.8% 

' ' after standing 15 hours 83 . 6 

48 " 83.6 

" " blowing with air 1 hour as soon as dissolved . . 83 . 5 

The commercial supply of carbon tetrachloride contains more 
or less carbon disulphide, and this naturally affects its solvent 
power, so that different lots may vary in this respect. As the carbon 
disulphide is much more volatile than the carbon tetrachloride, 
the majority of the latter can be removed by redistillation and 
rejecting all that which goes over below the boiling-point of 
the carbon tetrachloride, 76° C. It is also possible that it may 
be removed by blowing a current of air through the carbon tetra- 
chloride. 



METHODS OF ANALYSIS. 547 

Preparation of Pure Bitumen. — The preparation of the pure 
bitumen is a necessity where the percentage in the crude or refined 
material does not exceed 50 per cent, as under these circumstances 
its properties are so much concealed by the materials which are 
mixed with it that it is impossible to determine them, especially 
the hardness, softening point, and other physical data. The 
process which has been worked out for this purpose applies equally 
well to native bitumens and to artificial mixtures, such as old 
surfaces where it is desired to determine the consistency of the 
bitumen in the pavement. 

Such an amount of crude, refined material or old surface is taken 
as analysis shows will afford about 20 grams of pure bitumen. 
At the same time 20 grams of a bitumen or asphalt cement of 
corresponding character and of known consistency is taken and 
treated in the same way as the material under examination. This 
is done for a control, as will appear. The original material and 
that for the control determination are placed, in small pieces, 
in a 600 c.c. Erlenmeyer flask and covered with 300 c.c. of redis- 
tilled bisulphide of carbon. This with shaking is allowed to stand 
overnight or until all lumps are broken down and the bitumen 
is dissolved. After thorough sedimentation the solvent is decanted 
as carefully as possible into a litre flask and 200 c.c. of fresh bisul- 
phide poured upon the residue. This should be shaken and allowed 
to stand again until the insoluble matter has subsided, when the 
solution of bitumen is decanted as before and added to the first 
300 c.c. This process is renewed with several portions of 100 c.c. 
of bisulphide until the residue is clean. The entire solution is 
allowed to stand overnight, again decanted from the finer sedi- 
ment of mineral matter, and then swung in a centrifugal machine 
to remove as much of the still finer mineral matter as possible. 
If organic debris is present the solution must also be filtered, 
In case a more rapid method is desired for old surface mixtures, 
it is probably quite as satisfactory to swing the solution obtained 
in the first 300 c.c, as this is, of course, representative of the 
total bitumen, although only a portion of it. 

If no centrifugal is available the different bisulphide solutions 
are well mixed, allowed to stand for some days and decanted. 
The solutions of bitumen, the one holding that under examina- 



548 THE MODERN ASPHALT PAVEMENT. 

tion and the control, are, one after the other, placed in the same 
flask and the solvent distilled off as far as possible at the heat 
of a steam-bath. The hot and thick residue is poured into an 
iron dish, the 6-inch-deep-form sand-bath already described. 
This is placed on a suitable sized hole on the steam-bath and 
heated. The remaining bisulphide is largely driven off in this 
way. To prevent the vapor from the hot bisulphide from taking 
fire, it will do so without the presence of flame in contact with 
a hot steam-pipe, or from foaming over, a current of dry steam 
is blown over the surface of the liquid as long as vapor is evolved. 
Finally, the presence of the last traces of vapor are tested for 
with a small flame such as is used for determining the flashing- 
point of oils. If all vapor of bisulphide which can be distilled 
in this way has disappeared, the bitumen is in a condition to be 
brought over a flame or sand-bath and heated, with constant 
stirring, to a temperature depending on its softness, and until it is 
sufficiently fluid to be poured into a tin box for further treatment. 
This temperature should in no case exceed 325° F. These tin 
boxes are of the kind used in taking samples of asphalt cement 
for penetration and shipping them to the laboratory. A con- 
venient form and size is the flat, 2-oz., screw top, Gill style. 1 

The bitumen or bitumens Under examination and the control 
bitumen, after having been well identified in the tin boxes, are 
brought to the standard temperature and their consistency 
determined with the penetrometer. The control will usually 
be found to be softer by twenty or more points than in the original 
condition. If this is the case both or all of the extracted bitu- 
mens are put in an oven and heated for a length of time to 300° F., 
depending upon their excess of softness. It is important, of 
•course, that the conditions in the air-bath are uniform, and that 
the same precautions should be used as in the determination of 
loss at 325° F. and 400° F., as previously described. 

When the control bitumen has reached its original known 
consistency it is assumed that the bitumen or bitumens under exam- 
ination have done the same thing, and the product is taken as the 
pure bitumen as it occurs in its original consistency in the crude or 
refined material or of the cement as it exists in the surface mixture. 
1 American Can Co., New York. 



METHODS OF ANALYSIS. 



549 



Experience shows that this determination is reliable within 
five points on duplicate determinations. 

Fixed Carbon. — The fixed carbon is determined usually on 
the pure bitumen according to the method recommended by the 
Committee on Coal Analysis of the American Chemical Society and 
published in the Journal of the Society for 1899, 21, 1116. It is 
as follows : 

Place 1 gram of pure bitumen in a "platinum crucible weigh- 
ing 20 or 30 grams and having a tightly fitting cover. Heat 
over the full flame of a Bunsen burner for seven minutes. The 
crucible should be supported on a platinum triangle with the bottom 
6 to 8 cm, above the top of the burner. The flame should be 
fully 20 cm. high when burning free, and the determination 
should be made in a place free from draughts. The upper surface 
of the cover should burn clear, but the under surface should remain 
covered with carbon." 



FIXED CARBON IN BITUMENS. 



Grahamite 

Albertite 

Gilsonite 

Manjak, Barbadoes 

Asphaltenes from Trinidad bitumen 

Glance pitch 

Asphalts 

Byerlyte (artificial asphalt) 

Standard Asphalt Co.'s mine — soft gilsonite. 

Malthenes from Trinidad bitumen 

Wurtzilite, Utah 

Residuum, Pennsylvania field 

Sunset oil, Kern Co., Cal 



Extremes. 


High. 


Low. 


53.3 
54.2 
26.2 


35.3 

29.8 
3.3 


30'.6 
17.9 


is'.o 

10.8 


'8'.8 


*5*.3 


.... 


..„. 



High 

Grade. 



53.3 

29.8 

14.5 

25.0 

25.8 

15. 1 

14.2 

14. 

7. 

6. 



1 Egyptian. 

The residue minus the small impurity of ash in the pure bitumen 
is the fixed carbon, which should be calculated to 100 per cent with 
the volatile hydrocarbons, excluding the inorganic matter. As 
the committee states, this determination, like most industrial 
ones, is arbitrary, but it is of the greatest value in determining the 



550 THE MODERN ASPHALT PAVEMENT. 

nature of a bitumen quickly. Experience has shown that true 
hard asphalts have never been found which yielded more than 
17.9 per cent or less than 10.0 per cent of fixed carbon ; while 
grahamite yields over 53 per cent, albertite over 29 to 54 per cent, 
and some other bituminous materials characteristic amounts of 
fixed carbon. 

Examination of Heavy Petroleum Oil. 

Fluxing Agents and Oils. — The examination of materials 
under the above heading includes the determinations given in the 
accompanying forms: 

NEW YORK TESTING LABORATORY. 

Maurer, N. J., 

Report on sample of Fluxing Agent received from. . . . 



Character of flux 

Date when sample was gathered 

Name of manufacturer 

Tank-car number 

Sample number Test number 

Specific gravity, Beaume = Actual At 78° F. 

Flash-point ° F 

Loss, 212° F., . .hours 

Loss, 325° F., 7 hours 

Loss, 400° F., 7 hours 

Character of residue at 78° F 

Bitumen insoluble in 88° naphtha, air temperature. — Pitch. . 
Per cent of soluble bitumen removed by H 2 S0 4 

Paraffine scale 

This material is quality 

Remarks: 



METHODS OF ANALYSIS. 551 

NEW YORK TESTING LABORATORY. 
Maurer, N. J., . . 



Test number: 
Source of supply. 



Physical Properties. 

Specific gravity, dried at 212° F., 78° F./78° F 

Flows, cold test. 

Color 

Odor 

Under microscope 

Flashes, F. f N. Y. State oil-tester 

Viscosity 

Chemical Characteristics. 

Original substance: 

Loss, 212° F., 1 hour or until dry 

Dry substance : 

Loss, 325° F., 7 hours , 

Character of residue , 

Penetration of residue at 78° F. . . . , 

Loss, 400° F., 7 hours (fresh sample) , 

Character of residue 

Penetration of residue at 78° F , 

Bitumen soluble in CS 2 , air temperature , 

Difference 

Inorganic or mineral matter 

Bitumen insoluble in 88° naphtha, air temperature. — Pitch. 

Per cent of soluble bitumen removed by H 2 S0 4 

Per cent of bitumen as saturated hydrocarbons 

Per cent of solid paraffines 

Bitumen yields on ignition: 

Fixed carbon ., 

Ultimate composition: 



Remarks: 



552 THE MODERN ASPHALT PAVEMENT. 

The methods used in making these determinations are, as a 
whole, the same as those described for hard asphalts with the 
following modifications. 

Specific Gravity. — The specific gravity of oils or fluxes is 
taken on the material either dried at 212° F., or, if there are light 
oils present, volatile at this temperature, on some of the oil freed 
from water by being swung in the centrifugal. 

Heavy fluxes too dense to employ a picnometer with are filled 
into an open specimen tube, 10 cm. long, 2 cm. in diameter, 
and holding about 27 grams of water, even with the top, which 
is ground flat and parallel to the base. The weight of this volume 
of oil at 78° F. is compared with that of water at the same tempera- 
ture. Lighter oils are examined with the picnometer or Westphal 
balance. The industrial methods for the determination of the 
specific gravity of dense oils admit of much improvement and are 
now probably not accurate beyond the second place of decimals. 
Mr. Lester Kirschbraun, chemist of the Chicago City Labor- 
atory, Bureau of Engineering, describes the following method 
which is employed by him satisfactorily. 

Take a test tube about a half inch in diameter and cut 
it off to give a If inch by J inch tube. Flare it out to carry a 
fine wire. Put about 10 grams of the oil or asphalt into it, 
and suspend it in an oven to remove air bubbles and drive off the 
water. Cool and weigh accurately in air and immerse in distilled 
water at 25° C. to a fixed mark on the wire and weigh. Previous 
to filling the tube with the sample, determine its weight carefully 
in air and in water at 25° C, immersed to the fixed mark. These 
weighings give the weights of the tube alone, in air and 
in water, and the combined weights of the tube and the sample, 
in air and water. The gravity is calculated in this way, represent- 
ing, 

Weight of tube in air a 

Weight of tube and sample in air & 

Weight of tube in water c 

Weight of tube and sample in water d 

Wt. in air of sample 

top. £T. = ^ ■ 

Loss of wt. in water 



METHODS OF ANALYSIS. 553 

in this case becomes 

....... (1) 



(p-a)-(d-c) 

When the gravity of the sample is less than unity, the second 
expression in the denominator is a negative (d— c)quantity and 
is added to the original weight of the sample (b — a), inasmuch as 
the buoyancy of the sample will overcome its own weight and 
to a certain extent will also reduce the weight of the tube in water, 
making c greater than d. 

The formula in this case may be also expressed so: 

(2) 



(b-a) + (c-d) 

When the gravity of the sample is greater than unity, d 
will be greater than c and the first formula applies without 
confusion. As an example, take a blown oil, the gravity of which 
was determined in our laboratory according to this method. 

Weight of tube in air a = 4 .7870 

Weight of tube and sample in air b = 16 .7900 

Weight of tube in water, 25° C c = 2 .8565 

Weight of tube and sample in water d — 2 . 6425 

by formula (2) 

16.7900-4.7870 12.0030 

P * gr * _ (16.7900-4.7870) + (2.8565-2.6425) ~iX2T70 

This may seem a bit complicated at first, but it will be noted 
that the factors a and c are constants which can be used 
for the same tube without change, and the calculation becomes 
very simple after a few trials. 

The advantages of the method are in doing away with the 
inconveniences of handling a large amount of oil, and the ease 
with which air bubbles can be removed, particularly in handling 
refined asphalt. Of course it can be used only with oils which 
are viscous enough to be retained in the tube when under water. 



554 THE MODERN ASPHALT PAVEMENT. 

Flow Test. — Some of the oil is chilled in a large test-tube and 
gradually allowed to attain the temperature of the room. The 
point at which it will flow in the inclined tube is the flow-point. 

Color. — This is found by examining the reflection from the 
surface of the cold oil. It is intended to be that revealed by 
reflected and not by transmitted light through a thin film. 

Odor. — The odor can be described as that corresponding to 
different kinds of known petroleum in the cold or on heating. 

Microscopic Examination. — The appearance of an oil that has 
been heated is noted under the microscope to determine the presence 
of material insoluble in the main mass of the oil. 

Flash-point. — The flash-point is determined in a New York 
State oil-tester. 1 The water-bath is of course removed and the 
oil heated directly with a flame of a size to raise the temperature at 
the rate of 20° per minute and a small flame from a capillary glass 
or metal tube is used for flashing. The flame should be applied 
at 5° intervals. The determination should be repeated on such oils 
as flash at unexpected temperatures. The water must be removed 
from the oil or flux before putting it in the tester cup, either by heat 
or by the centrifugal. 

Open tests of high flashing oils are not reliable and at the 
best with the closed tester a reading of 5° intervals only need be 
sought. 

Viscosity. — The Engler viscosimeter is used for this purpose, 
it being available for temperatures as high as 500° C. 

The rate of flow in seconds of time is compared with that of 
an equal volume of water at the same or some standard tem- 
perature. 

Loss at 212° F. — The water or loss of light oils at 212° F. is 
determined by weighing out 20 grams in a glass or tin dish, such 
as is described for use in the determination of loss at 325° F. in 
hard asphalts, and heating in the oven described, at the temper- 
ature named, until the oil has ceased foaming, or to practically 
constant weight. The precautions previously noted should be 
observed. When oils contain a large percentage of water this is 

» E. & A., No. 4160. 



METHODS OF ANALYSIS. 555 

better determined by the centrifugal method or by dilution with 
naphtha. 

Drying an oil or flux for subsequent examination is done by 
heating a large volume in an iron dish over a flame, with constant 
stirring, unless it contains much light oil, when the centrifugal 
method alone can be used. 

Loss at 325 F. and 400 F. in Ssven Hours. — Separate portions 
of 20 grams of the dried material are taken for each determina- 
tion and are heated to these temperatures in the manner described 
for solid bitumens. The residues from the oils and fluxes are 
examined after heating to these temperatures more in detail than 
those from hard asphalts which have been treated similarly. 

After cooling and weighing the appearance of the residue is 
noted, especially as to whether it is smooth. or granular owing to the 
presence of paraffine, the temperature at which it flows, whether 
it pulls out to a long string or is short. If it is so hard that it does 
not flow except on raising the temperature above 100° F., its con- 
sistency is determined with the penetrometer either at 100° F. or 
at 78° F. or at lower temperatures. 

The residue should also be examined under the microscope to 
determine whether, owing to the nature of the fluxes, they have 
been at all decomposed at these temperatures with a separation 
Of insoluble pitch, which is an evidence that the original flux must 
have been more or less cracked in the process of manufacture. 

Total Bitumen ; Inorganic Matter and Naphtha Soluble Bitu- 
men. — These determinations are arrived at by the methods 
already described for hard asphalts. 

As the oils and fluxes are more easily soluble it is unnecessary 
to let the solvents act on them for so long a time as in the case 
of hard asphalts. There is little object in using 62° naphtha with 
oils or fluxes, as there is too little difference between its solvent 
power and that of bisulphide of carbon with such materials to make 
it worth while. The residue insoluble in 88° naphtha, however, 
shows how much decomposition there has been in fluxes which 
have been subjected to excessive heat. 

Determination of the Character of the Hydrocarbons in Fluxes. 
— The character of the hydrocarbons in any of the heavy oils used 



556 THE MODERN ASPHALT PAVEMENT. 

for fluxing purposes is determined by treatment with sulphuric 
acid after the method described for use with malthenes from hard 
asphalts. 

Determination of the Amount of Hard Paraffine Scale. — The 
amount of hard paraffine scale contained in any flux or heavy 
oil can be readily determined by the author's modification 1 of 
the method of Holde. 2 

The method in detail is as follows: 

The Determination of Paraffine in Petroleum Residues, 
Asphaltic Oils, and Asphalts Fluxed with Paraffine Oils. — For 
this purpose, one, two 7 or more grams, of the substance to be ex- 
amined is taken and covered in an Erlenmeyer flask with 100 c.c. 
of 88° naphtha. The amount will depend on the paraffine present 
and on the percentage of oil which remains after the preliminary 
treatment with naphtha and acid. Of a residuum from east- 
ern pipe-line oils one gram is sufficient, as the substance con- 
sists of a nearly pure bitumen containing from 4 to 12 per cent of 
paraffine. Ten grams of a residual pitch from asphaltic oil should 
be used, as this, in some cases, contains only 65.0 per cent of its 
bitumen soluble in naphtha, less than 50 per cent unacted on by acids, 
and only about 1.0 per cent paraffine. Several grams can be taken 
of a Trinidad asphalt cement, made of asphaltum and paraf- 
fine residuum, which contains 26.0 per cent of mineral matter 
and only 70.0 per cent of its bitumen is in a form soluble in 88° 
naphtha. 

The object of the naphtha treatment is to separate the paraffine 
from substances of a non-bituminous nature and from some of 
the asphaltic hydrocarbons insoluble in naphtha which would 
be precipitated in the ether alcohol solvent and contaminate the 
paraffine. 

By this means all the unsaturated hydrocarbons and those 
of an asphaltic nature, readily precipitated by alcohol from 



1 J. Soc. Chem. Ind., 1902, 21, 690. 

2 Mitt. a. d. Konig, tech. Vers-anst, Berlin, 1896, 14, 211. Abs. J. Soc. 
Chem. Ind., 1897, 16, 362. Lunge, Chem. tech., Untersuchungs, Methoden. 
3.9. 



METHODS OF ANALYSIS. 



55^ 



their ether solution, are removed and the possibility brought 
about of recovering the paraffine in a pure condition. 

Some determinations made in the manner described resulted 
as follows : 



PETROLEUM RESIDUUM FROM PIPE-LINE OIL. 

Specific gravity, 0.93. 



Number. 


Weight 
taken. 


Soluble in Naphtha. 


Not acted on by 
H2SG-4. 


Paraffine. 


1 

2 
3 


Grams. 

1.0 
1.0 
1.0 


Per Cent. 
96.0 

96.0 
Distilled in vacuo 


Per Cent. 
No treatment 

89.5 
No treatment 


Per Cent. 
7.95 
5.55 
5.95 


TRINIDAD ASPHALT CEMENT. 


Number. 


Weight Taken, 
Grams. 


Soluble in Naphtha. 


Not Acted on by 
H 2 S0 4 . 


Paraffine. 


1 

2 


10.0 
10.0 




No treatment 
Treated 


2.95 
0.95 



In each case the paraffine recovered after treatment was white 
and pure, while that obtained in the other way, even by distilla- 
tion in vacuo, was colored. The results after treatment were, of 
course, lower and more correct. 

The Trinidad asphalt cement was made from 100 parts of 
Trinidad asphalt and 20 parts of a residuum similar to the one 
analyzed. The asphalt contained, of course, no paraffine; the 
residuum, 5.55 per cent. The calculated amount in the cement 
is therefore 0.925 per cent, and 0.95 per cent was found. 

In this way it can be determined whether the flux which has 
been used in the preparation of an asphalt cement has been derived 
from paraffine petroleum or from one having an asphaltic base, 
since if paraffine is found to such an extent as shown above it win 
necessarily point to the use of a paraffine flux, as no native solid 
bitumen in use in the paving industry contains paraffine. 



558 THE MODERN ASPHALT PAVEMENT. 

Rapid Method for Paraffine in Crude Petroleum Fluxes and 
Residues. 1 Standard Oil Company. — The preceding method, while 
not lacking in accuracy, cannot be completed in a single day, and 
the following method, while yielding lower results, has the ad- 
vantage of rapidity. 

One hundred grams of the oil is distilled rapidly in a 6-oz. 
retort to dry coke. 

Five grams of the well mixed distillate is treated in a 2-oz. flask 
with 25 cc. Squibb's ether; after mixing together thoroughly, 
25 cc. Squibb's absolute alcohol is added, and the flask packed 
closely in a freezing mixture of finely crushed ice and salt for at 
least thirty minutes. Filter off the precipitate quickly by means of 
a suction pump, using a No. 575 C. S. & S. 9-cm. hardened filter, 
cooled by the above freezing mixture in a suitable apparatus. 

Rinse and wash the precipitate with 1 to 1 Squibb's alcohol 
and ether mixture, cooled to 0° F. until free from oil. Fifty cc. 
of the washed solution is usually sufficient. When sucked dry, 
remove the paper, transfer the waxy precipitate to a small glass 
crystallizing dish. Dry on a steam bath and determine the 
weight of paraffine scale remaining in the dish. 

Calculation. — Weight of paraffine scale divided by weight of 
distillate taken and multiplied by per cent of total distillate ob- 
tained from original sample, equals per cent of paraffine scale. 

Fixed Carbon. — This determination is sometimes desirable 
with fluxes, especially with harder ones, to show the same facts 
revealed by the 88° naphtha extract. It is carried out in the 
same way as with hard bitumen. 

Asphalt Cement. — Asphalt cement is examined to determine 
its consistency, the amount of bitumen, inorganic or mineral 
matter and organic matter, not soluble, it contains. Rarely the 
naphtha soluble bitumen is extracted and examined to determine 
the nature and quantity of the flux of which it has been made. 
The permanency of its consistency, when it is maintained in a 
melted condition at 325° F. for some time, may be noted. 

# The consistency of asphalt cement is determined in several 
ways, the most desirable of which in the laboratory is the pene- 

1 Kindly furnished by Mr. George M. Saybolt. 



METHODS OF ANALYSIS. 559 

tration machine, for the reason that it admits of an absolute record 
in figures. Penetration machines have been designed by Bowen, 
Kenyon, Dow, and the New York Testing Laboratory. The two 
latter, however, have superseded the earlier and less desirable types. 

The flow test originated by the Warren-Scharf Asphalt Paving 
Company, as well as the test by chewing, which is a rough one 
but always available, are of decided value and convenience for 
use at plants. 

The construction of the various penetration machines and the 
method of using them is described as follows : 

Bowen's Penetration Machine or Viscosimeter for Bitumi- 
nous Solids. — Principle of the Machine. — The machine, Fig. 34, is 
designed to register on a dial in degrees, arbitrarily selected, the 
depth to which, a No. 2 cambric needle, attached to a weighted 
arm or lever, penetrates into the surface of the material to be 
tested when allowed to act upon it for one second at a standard 
temperature. 

The machine has been described by IT. C. Bowen, in the 
School of Mines Quarterly, 10, 297. 

The Dow Penetration Machine. — A penetration machine has 
been designed by Mr. A. W. Dow, formerly Inspector of Asphalt and 
Cements, of the District of Columbia, Washington, D.C., which in so 
far as it is based on the measurement of the millimeters to which a 
definite needle penetrates into the asphalt cement under a definite 
weight at a definite temperature is concerned, is a more truly 
scientific instrument than the one previously described. The read- 
ings by this machine are about 20 points lower than those obtained 
with the Bowen instrument, but it possesses the disadvantage 
that when large numbers of asphalt cements are to be examined 
at any one time it requires greater delicacy of manipulation and 
much more time than is the case when the Bowen machine is 
used. Fig. 35. Mr. Dow describes its use as follows: 

" Description and Directions for Using the Dow Penetration 
Machine. — The object of the penetration test is to ascertain the 
softness of asphalt, etc., and is accomplished by determining the 
distance a weighted needle will penetrate into the specimens under 
examination. 



560 



THE MODERN ASPHALT PAVEMENT. 




-^^ksmm^ 



Fia 34. — Bo wen Penetration Machine. 



METHODS OF ANALYSIS. 



561 



" So that all tests may be comparable, a standard needle 
should be used, weighted with a constant weight. The tests should 
be made on samples at a standard temperature and be made for 





Fig. 35. — Dow Penetration Machine. 



the same length of time in every case. The standards used in 
this machine for testing cements to see that they are of uniform 
consistency are a No. 2 needle, weighted with 100 grams, pene- 
trating for five seconds into the sample at a temperature of of 77° F. 
(25° C.) 

" The apparatus consists of a No. 2 needle A, inserted in a 



562 THE MODERN ASPHALT PAVEMENT. 

short brass rod which is held in the aluminum rod C by the 
binding screw B. The aluminum rod is secured in a frame- 
work so weighted and balanced that when it is supported on the 
point of the needle A the framework and rod will stand in an 
upright position, allowing the needle to penetrate perpendicu- 
larly without the aid of a support, thus doing away with any 
friction. 

" The frame, aluminium rod, and needle weigh 100 grams with 
the weight on bottom of frame ; without weight 50 grams. Thus 
when the point of the needle rests on the surface of the sample 
of material to be tested as to the penetration, it will penetrate 
into the sample under a weight of 100 grams or 50 grams as desired. 

" The needle and weighted frame are shown in Fig. 35, side 
and front views of the entire apparatus put together and ready 
for making a penetration. D is the shelf for the sample, E, 
is the clamp to hold the aluminum rod C until it is desired 
to make a test, F is a button which when pressed opens clamp E. 
By turning this button while the clamp is being held open it will 
lock and keep the clamp from closing until unlocked. The device 
to measure the distance penetrated by the needle consists of a 
rack, the foot of which is G. The movement of this rack up or 
down turns a pinion to which is attached the hand which indicates 
on dial K the distance moved by the rack. One division of the 
dial corresponds to a movement of the rack of 1/100 cm. The rack 
can be raised or lowered by moving counterweight H up or down. 
L is a tin box containing sample to be tested which is covered 
with water in the glass cup, thus keeping its temperature constant. 
MM' are leveling screws. A clock movement having a 10-inch 
pendulum is attached to the wall to one side of the machine. Make 
a mark P on the wall just at the extremity of the swing of the 
pendulum; a double swing of this pendulum, that is from the time 
it leaves P until it returns, is one second. 

" The only other things necessary to complete the outfit are a 
large dish-pan, a pitcher to hold ice-water and a tin for hot water; 
a coffee-pot is a good thing. 

" To make penetration tests place the materials contained in 
circular tins, along with the glass dish, under five or six inches of 



METHODS OF ANALYSIS. 563 

water in the dish-pan, which should have been previously brought 
to a temperature of 77° F. by the addition of hot water or cold 
water. 

" While the sample are under the water it should be stirred 
every few minutes, with the thermometer and the temperature 
kept constant at 77° F. by the addition of hot or cold water as the 
case may require. The samples should remain under the water for 
at least fifteen minutes and in cases where they are very cold or 
hot, at least one-half hour. The most expeditious way to proceed in 
testing a sample just taken from a still or tank is to immerse it in 
ice-water as soon as it has hardened sufficiently and keep it there for 
ten minutes, then in the water at 77° F. and keep it there for fifteen 
minutes. When the sample has remained in the water for the speci- 
fied time it is ready to penetrate. 

" The aluminum rod C should be pressed up through the clamp 
E so that it will be at such a height that the glass cup will easily 
pass under it when placed on shelf D. 

" A sample in tin box should now be placed in the glass cup and 
removed in it covered with as much water as convenient without 
spilling. 

" The glass cup containing sample is placed on shelf D under 
C. Insert brass rod with needle into C and secure by tightening 
binding screw B, lower C until the point of the needle very nearly 
touches surface of sample; then, by grasping the frame with two 
hands at S and S', cautiously pull down until needle is just in con- 
tact with surface of sample. 

" This can best be seen by having a light so situated that, 
looking through the sides of the glass cup, the needle will be reflected 
in the surface of the sample. After thus setting the needle, raise 
counterweight H slowly until the foot of the rack G rests on 
the head of rod C; note reading of dial, place thumb of right 
hand on R and press button F with forefinger, thus opening the 
clamp. 

" Hold open for five seconds and then allow it to close. The 
difference between the former reading of the dial and the present 
is the distance penetrated by the needle, or the penetration of the 
sample. Raise rack, loosen binding screw B raise rod through 



564 THE MODERN ASPHALT PAVEMENT. 

clamp, leaving the needle sticking in sample. Remove needle 
from sample, clean well by passing through a dry cloth, replace 
needle in C and the machine is ready for another test. 

" Do not clean needle on oily cloth, or waste. 

" Do not allow rack to descend too rapidly on rod C as it 
may force C through the clamp, thus spoiling the reading. 

" After using the machine, leave it so the top of the rack is 
just level with its base. You will thus prevent dust from entering 
and getting into pinion. When not in use keep machine covered 
with a cloth to protect from dust. 

" Examine point of needle from time to time with magnifying 
glass to see that it is not injured in any way. 

"If the needle is found defective remove by heating the brass 
rod, when the needle can be withdrawn with pincers. Break eye 
from one of the extra needles and press into brass rod previously 
heated. 

"If needle does not stay in well, insert it with a small lump of 
asphalt. 

"If when this framework is supported on the point of the 
needle it does not balance so that the aluminum rod C stands 
perfectly perpendicular, the frame is bent and should be straight- 
ened until the rod stands perpendicular. This can easily be done 
by hand. 

"If rack G does not descend readily of its own weight when 
counter weight H is raised, it is likely that dust has gotten into 
the pinion. To get at pinion to clean, remove dial K and bear- 
ing T, when pinion can be pulled out sufficiently far to clean. 

"Never oil rack and pinion, as it prevents a free movement 
of rack. 

"If machine is unsatisfactory write and explain trouble. 

"Test for Susceptibility to Changes in Temperature. — The 
standards that I have adopted for this test are: 

"The distance penetrated by the No. 2 needle into the sample 
at 32° F. in one minute with 200 grams on frame. 

"The penetration at 77° F., as described before, and the pene- 
tration into the sample of the No. 2 needle in five seconds at 100° F. 
with 50-gram frame. In some cases I use 100 grams, which 



METHODS OF ANALYSIS. 



565 



is preferable if the depth of the sample will permit. In all cases 
when you give a penetration of cement state in parentheses how 
it was made, as for example (No. 2N., 5 sec, 50 grams, 100°) 
means that the penetration was made with a No. 2 needle pene- 
trating 5 seconds with 50-gram frame at 100° F. 

"If a statement is made like this there can never be any doubt 
about the figures and they will be understood by all familiar with 
the machine." 

New York Testing Laboratory Penetrometer . — In the Dow in- 




Fig. 36. 



strument, all the parts are of very light construction and require 
a certain delicacy of touch to use it satisfactorily, and consequent- 



566 



THE MODERN ASPHALT PAVEMENT. 



ly, it is not easily manipulated by such men as are found at paving 
plants, although these disadvantages are of slight consideration 
in the laboratory. The shelf upon which the sample to be tested 
is placed is fixed and the needle must, therefore, be brought 




Fig. 37. 

down toward the surface of the bituminous cement until it is in 
contact with it. On each side of the shelf which holds the sample 
are the two rods of the frame from which the weight which acts 
upon the needle is suspended. These are much in the way in 
adjusting the needle in contact with the surface of the bituminous 
cement, and restrict the size of the sample of the latter. 



METHODS OF ANALYSIS. 567 

In the Penetrometer (Figs. 36 and 37), an attempt has been 
made to overcome these features, without seriously imparing the 
accuracy of the instrument. The sample to be tested, which may, 
if desired, be of large or small size, is placed upon a table which is 
supported upon a screw, enabling the needle to be set at zero, 
and the sample to be brought up to contact with the point by 
elevating it with the screw. The entire weight acting upon the 
needle is contained in the tube which holds it, and, being placed 
at the lowest possible point in the tube, does not tend to seriously 
divert it from the vertical on the release of the clamp and makes 
it possible to do away with the frame which is so much in the 
way in the Dow apparatus. The Penetrometer is given greater 
stability than the Dow apparatus by making a much larger and 
firmer clamp to hold the tube, while all the other parts of the 
instrument are rigidly constructed. The increased friction of 
the clamp on the rod reduces the extent of the penetration of 
the needle by one- or two-tenths of a millimeter, but this is prac- 
tically of no consequence, as it is a variation not greater than that 
due to different needles or to the personal equation of various 
operators. 

The determination of the depth to which the needle has pen- 
etrated is arrived at by a similar means to that employed in the 
Dow machine, a rack and pinion, but the rod to which the rack 
is attached is prevented from moving, not by a balance weight 
attached to a cord, as in the Dow machine, but by a spring ex- 
erting a slight pressure against its side. This does away with the 
opportunity for the cord and balance weight to be knocked out 
of place or lost, and makes the apparatus much more convenient 
to move from place to place. The penetration of the needle is 
registered in tenths of millimeters, on the same scale as in the 
Dow machine, and the time during which the weight acts is made 
five seconds instead of one, as is the case of the Bowen apparatus. 
The detail of the manipulation of the tests is the same with the 
Penetrometer as with the Dow apparatus, previously described. 

The Penetrometer is manufactured by Messrs. Howard & 
Morse, 1197 DeKalb Avenue, Brooklyn, N. Y. 

Flow Test. — The consistency of asphalt cements can also be 
controlled by means of a flow test. This is a comparative one 



568 



THE MODERN ASPHALT PAVEMENT. 



and gives nothing but ocular evidence as to the relative softness 
of two cements at or near their flowing point. The test consists 
in making, in a suitable mould, cylinders f inch long and f inch 
in diameter, of a standard cement and of the one to be examined, 
placing them on a brass plate with corrugations corresponding 
in size to that of the cylinders and exposing them at an angle of 
45° to a temperature at which the cements will soften and flow. 




Fig. 38.— Flow Plate. 
Cements made of the same asphalt and flux are of the same con- 
sistency if they flow to the same length, Fig. 38. 

As a quick, rough test this is very satisfactory; but care must 
be taken that the cylinders are exposed to a uniform temperature 
and that one part of the brass plate is not hotter than another, 
which may readily happen if it touches hot metal or any good 



METHODS OF ANALYSIS. 569 

conductor. The plate, for safety, should only be warmed by air 
and should be isolated from contact with metals by asbestos, paper 
or wood. 

Cylinders are made by softening the cement to be examined 
until it can be rolled out on a board to about the proper size. It 
is then pressed in a brass mould of the exact size, which is made in 
halves, and cut off to the right length with a hot knife. With any 
particular cement a weighed amount known to make a cylinder of 
proper size may be taken and rolled to the right length instead of 
using a mould. 

The cylinders, while still warm, are pressed upon the brass 
plate until they adhere and allowed to come to a constant tem- 
perature by immersion in water before warming for the flow test. 
The cylinders must stick to the flow plate in the beginning or they 
may slide instead of flow. The flow plates are 8x2| inches in 
size and have corrugations for four cylinders. As has been said 
the selection of some means of affording a uniform temperature is 
the most difficult one. In the New York Testing Laboratory, 
a carefully regulated rectangular air bath illuminated by a 
small incandescent bulb and containing a mica covered window 
in the door is employed. At the plants a box heated by a 
<!oil of pipe through which steam is conducted can be arranged; 
or, for rough work, the plate is placed over a stove with- 
out being in contact with the metal. In trying any new 
method of heating it is well to put duplicates of the same material 
on different parts of the plate and see if they flow alike. This will 
determine whether the oven is sufficiently uniformly heated for 
practical purposes. 

Flows of Trinidad asphalt cements are made at about 160° F., 
others at somewhat lower or higher temperatures, as the case may 
demand. One kind of cement cannot, of course, be compared with 
that made from another bitumen, even if they have the same pene- 
tration at 78° F. 

Composition of Asphalt Cement. — The percentages of bitumen, 
organic insoluble matter and inorganic or mineral matter in all 
asphalt cements can be determined exactly as in refined asphalts. 

The naphtha soluble bitumen is sometimes sought with a view to 



570 THE MODERN ASPHALT PAVEMENT. 

its examination and the determination of the nature and amount of 
flux which has been used in making the cement. This is done in the 
same way as with refined asphalts or fluxes, but the naphtha 
solution is evaporated and the residual bitumen examined. Al- 
though it will contain the malthenes of the asphalt as well as those 
of the flux used in making the cement, the percentage of the former 
being known for any given asphalt, it is possible to calculate the 
latter if the cement has not been maintained at a high temperature 
in a melted state for too long a time with volatilization and loss of 
oil. From the physical characteristics and distillation the nature 
of the flux can generally be determined as between an eastern 
or California residuum, and the presence of coal-tar or dead-oil 
is easily detected. 

The bitumen in asphalt cements holding much organic matter 
can be estimated onty by percolation with the Gooch crucible, 
but in Trinidad and other cements carrying much mineral matter, 
when examined in large number, the bitumen can be more expedi- 
tiously determined by the centrifugal machine. The centrifugal 
machine in use for this purpose in the New York Testing Labora- 
tory, at Maurer, N. J., is a large Troy laundry extractor with a bas- 
ket 30 inches in diameter, which has been filled about the circum- 
ference with solid boxwood, leaving an opening 11 inches in 
diameter in the centre. In this boxwood are bored about three 
dozen one-inch holes to a depth of 6J inches, sloping downward 
at an angle of 15°, provided with metal liners, in the bottom of 
which a piece of sponge is placed to form a cushion with water, and 
which in turn hold the glass tubes, about 1 inch in exterior diameter 
and 8 inches long, weighing 50 to 60 grams, in which, after being 
accurately weighed, is placed 1 gram of the asphalt cement stirred 
up with bisulphide of carbon to reach to a height not greater than 
4J to 4 J inches in the tube and amounting to 30-35 c.c. of solvent. 
The tubes and substance thus prepared are placed in the centrifugal 
in such a way as to balance the basket and the power is applied 
to give a revolution of 1500 per minute. This is kept up for fifteen 
minutes, when the tubes are taken out and decanted carefully, with- 
out pouring off any sediment into flint 8-ounce wide-mouth bottles 
labelled with the same number as the tubes. More bisulphide of car^ 



METHODS OF ANALYSIS. 571 

bon is then added, the sediment thoroughly mixed with it by means 
of an iron rod, which is afterwards washed off with the solvent, 
and the tubes again placed in the centrifugal and run ten minutes. 
The decanting is repeated into the correction bottle, more solvent 
added as before, and the tubes swung a third time. The third 
decantation usually leaves the residue free from any amount of 
bitumen which would influence the results. The tubes are placed 
in a warm spot to volatilize the remaining solvent and when dry 
are weighed. In the meantime the bisulphide of carbon solution 
is burned for a correction, as in the analysis of refined asphalts, 
and the weight added to that of the tube. The loss of weight of 
the tube gives the percentage of bitumen in the cement. 

An excellent power centrifuge holding six tubes which is 
driven by electricity is furnished by the American Name Plate 
Company, 62 Sudbury Street, Boston, Mass. 

Change in Consistency of Asphalt Cements on Maintaining 
in a Melted Condition. — This change can be found by heating some 
of the cement to any desired temperature, as in the determination 
of loss at 325° F. in fluxes and making penetrations before and 
after heating. 

This treatment, however, is much more severe than any that 
a cement would ever receive at a plant, as the surface, as com- 
pared to the volume under treatment, is very much larger than 
is the case in a melting-kettle or dipping-tank. Such determina- 
tions are, in consequence, of relative value only in comparing 
cements made with different fluxes. 

Mineral Aggregate. — The mineral aggregate is determined in 
the same manner as in solid bitumens. 

Examination of the Finished Surface Mixture. — Samples of 
surface mixture are examined as to the per cent of bitumen they 
contain and the grading of the mineral aggregate. 

Bitumen. — The amount of bitumen is determined in one of two 
ways: 

1. A funnel, 2| inches in diameter, with a short stem, is placed 
in a conical flat-bottom assay flask, holding about 250 c.c. 
A Schleicher & Schull 9 cm. 597 filter-paper is folded and placed in 
foe funnel. Ten grams of the surface mixture are weighed out 



572 THE MODERN ASPHALT PAVEMENT. 

in fair-sized pieces on the balance to be described later and placed 
upon the filter. With a washing-bottle provided with two tubes 
through its cork, one reaching to the bottom of the bottle and the 
other only just passing the cork, but with a capillary orifice, a 
small stream of bisulphide of carbon can be delivered on inverting 
the flask without the necessity of using pressure from the mouth 
and inhaling the noxious vapor of the solvent. With this bottle 
a fine stream is directed on the surface mixture, but no more than 
it can absorb. It is allowed to stand until it has softened and 
settled upon the filter. The latter is then filled up to an eighth 
of an inch below the rim and the funnel covered with a 2i-inch 
watch-glass. It is not filled up at first, as before the mixture has 
been softened and settled upon the paper the solvent would have 
run through the filter-paper and would not have been used econom- 
ically. As the percolation goes on the solvent is renewed, and 
if it goes too slowly the rate may be hastened by washing between 
the paper and the funnel with bisulphide, which will dissolve the 
bitumen, which may have hardened and closed the pores by evapo- 
ration, or by lifting the filter a little and letting it drop back. 
On the day the analysis is started the sand is washed as clean as 
possible, but nothing more is done. The filter with the sand and 
the percolate is allowed to stand overnight to permit anything 
that has run through to settle out. 

In the morning the funnel is placed in a clean assay flask and 
the percolate is carefully decanted into a correction bottle, being 
careful not to disturb the sediment. 

Some bisulphide of carbon is poured on this, it is shaken up 
and poured back on the filter, the first assay flask being thoroughly 
cleaned with a feather and everything brought upon the original 
filter-paper. The mineral aggregate is washed clean with the solvent. 

The percolate, or solution of bitumen, in bisulphide of carbon 
is poured from the correction bottle into a dish, burned, ignited, 
and the correction obtained. 

In the meantime the mineral aggregate after drying is separated 
from the filter over a piece of glazed paper by scraping with a 
blunt spatula or rubbing between the fingers in an appropriate way 
until all the mineral matter that can be removed is separated, 



METHODS OF ANALYSIS. 573 

taking care, of course, not to detach any fibres of the paper. It 
is then dusted into a weighed No. 2 Royal Berlin porcelain crucible 
and set aside. The filter-paper, containing much fine mineral 
matter in its pores, is burned either with the correction in its dish 
or in any satisfactory way, its ash and the correction added to the 
mineral aggregate and the crucible's entire contents, after one 
is assured that no trace of solvent remains, is weighed. The 
difference in the weight of the aggregate and the ten grams of 
surface taken is that of the bitumen and gives the per cent of 
bitumen in the mixture, which should be calculated to the nearest 
tenth of one per cent. The expression of the percentage in hun- 
dredths is beyond the limit of accuracy of the method and is 
cumbersome and unnecessary. 

Centrifugal Method for the Examination of Surface Mix- 
ture. — In laboratories where large numbers of surface mixtures 
are examined daily, as in that of the author, where the number 
has reached 70, the centrifugal method as described on page 570 
is commonly used. Ten grams of the surface mixture are weighed 
out in a glass tube and submitted to the same treatment as is 
applied to asphalt cements. The loss of weight of the tube minus 
that of the correction obtained on burning the extracted bitumen 
gives the percentage of bitumen in the mixture. Should the 
mineral aggregate contain coal or other material too light to 
be thrown out by centrifugal action, the decanted bisulphide 
must be filtered before burning or the percolation method alone 
can be used. 

Grading of the Mineral Aggregate in a Surface Mixture. — The 
mineral aggregate from the porcelain crucible after having been 
weighed for the determination of bitumen or the mineral matter 
from the glass tube which has been submitted to the centrifugal 
process is emptied upon the 200-mesh sieve. The particles of 
dust, which are caked together, are broken up by gentle pressure 
with the finger tips and the coarser sand grains thoroughly cleaned 
by attrition. When nothing further passes the sieve the residue 
is transferred in any convenient way to the pan of a balance, 
preferably one which, while weighing accurately to a hundredth 
of a gram or one-tenth per cent of the amount of surface mixture 



574 



THE MODERN ASPHALT PAVEMENT. 



taken, does not require the use of weights but can be rapidly 
manipulated. 

Such a balance is supplied by the C. H. Stoelting Co., 31 W. 
Randolph St., Chicago, 111., or Eimer & Amend, New York, in the 
Chaslyn balance, Fig. 39. This is a beam balance, very much of 
the Westphal specific gravity type, which weighs readily to 10 mgs. 
by moving rings of different weight along the beam. It is exactly 
suited for rapid work with surface mixtures where results no closer 
than i l -$ of 1 per cent are sought. With this balance the weight 




Fig. 39. — Chaslyn Balance, 
of the residue on the 200-mesh sieve is obtained and the differ- 
ence between this and the weight of the mineral aggregate gives the 
percentage of 200-mesh material and filler in surface mixture. It is 
a determination by loss, and so no effort is necessary to save the 
dust which passes the sieve, unless it is desired tc determine its 
chemical nature or subdivide further by elutriation when it 
should be caught in a closely fitting pan. 



METHODS OF ANALYSIS. 



575 



The other sieves are used in succession after the 200-mesh 
with the precautions mentioned under sands and the percentages 
passed by each determined. 

The percentage of bitumen, dust, or filler, and various sized 
sand should amount to 100 per cent. 

The results are reported on the following form: 

NEW YORK TESTING LABORATORY, 

Maurer, N. J., , 

Mesh composition and quality of 

Received from , 



Test No. 
Test No. 
Test No. 
Test No 



Sample No. 
Sample No. 
Sample No. 
Sample No. 



Test N 


o. 














Standard Mixture. 


MesL 
No. 


Per Cent. 


Per Cent. 


Per Cent. 


Per Cent. 


Heavy 
Traffic 


Light 
Traffic 


Pass- 
ing 


Total 


Pass- 
ing 


Total 


Pass- 
ing 


Total 


Pass- 
ing 


Total 


10.5 

13.0 

S:S}»-» 

24.0 
11.0 

8.0] 

5.0 M6-0 

3.0J 


10.0 
10.0 

}l8.0 

[24.0 
On 


Bit. 
200 
100 
80 
50 
40 
30 
20 
10 

10 



















Penetration of A. C. 

Pat paper stain. . . . 

Remarks: 



576 THE MODERN ASPHALT PAVEMENT. 

Method for the Examination of Asphaltic Concrete and As- 
phalt Blocks. — The quantity of concrete which should be taken 
for the analysis will depend upon the size of the largest particles 
of the mineral aggregate. 

Three hundred grams of an asphalt block, 500 grams when 
the largest particles range from \ to J inch, or 1000 grams when 
1 inch particles predominate, will be sufficient. Several com- 
parative analyses of the latter class, employing respectively, 1, 
2, and 10 kilos of the sample, were in very close agreement. 

In order to retain the original relation of the various particles 
of the mineral aggregate, it is obvious that none of the stones 
should be fractured in taking the portion for analysis, and the 
sample should accordingly be softened by heating so that it may 
readily be broken apart by hand. 

Analysis by Decantation. — An appropriate amount of the 
sample is placed in a metal beaker or measure, covered with 
carbon disulphide and allowed to settle for two hours; decant 
and cover with fresh carbon disulphide; repeat this treatment 
until the solution becomes clear. 

Burn off the carbon disulphide to recover the mineral matter 
carried over with the extract, in a platinum or porcelain dish. 
Dry and weigh residue together with the correction. The loss 
from weight of concrete taken is bitumen. 

The mineral aggregate may now be further examined by care- 
fully compacting in a suitable vessel to determine the amount 
of voids or sifted through a series of perforated metal and wire 
cloth screens to ascertain the size of the various particles or its 
grading. 

Centrifugal Method. — While the preceding method is not lack- 
ing in accuracy, when intelligently manipulated, it is far from 
rapid, especially when a large mass of material is under considera- 
tion, and more or less extravagant in the use of solvent. The 
following method has therefore been developed, applying the 
essentials of the special centrifugal extractor as closely as they 
could be gathered from a brief verbal description, very kindly 
supplied by its ingenious inventor, Mr. August E. Shutte. 

The body of the apparatus consists of a double walled iron 



METHODS OF ANALYSIS. 



577 



casting, the inside dimensions of which are 9^ inches diameter by 
7 inches deep, set upon three legs and provided with a tightly 
fitting cover carrying a reservoir, also consisting of a single cast- 
ing. The combined portions form in effect a large Soxhlet 
extractor, as will be observed upon inspection of the illustrations, 
Figs. 40 and 41. 




Fig. 4a 

A slotted shaft extends through the bottom of the extractor 
and a gland is provided for making a tight joint. This, as well as 
the gasket under the cover, may be packed with ball lamp wicking 
and soap. 

The sample is broken down as finely as practicable and placed on 



578 



THE MODERN ASPHALT PAVEMENT. 



the cast iron plate which fits upon the end of the slotted shaft. A 
filter ring cut from No. 80 soft roofing felt about .090 inches thick 




Fig. 41. 



is placed under the rim of the dome, which is now bolted down 
hard upon the plate over the sample. Fig. 42. 

A dome 8 inches diameter by 3| inches high, spun out of No. 16 
brass, will accommodate one kilogram of concrete. The plate is 



METHODS OF ANALYSIS. 



579 



8i inches diameter. The bolt should be tool steel, T ^ inch 
diameter. A shallow brass pan is placed in the device to receive 
the extract as it is thrown out of the revolving dome. 

The dome having been placed in position upon the shaft, about 
300 cc. carbon disulphide is poured upon the sample through the 
perforations in the top and the apparatus closed. 

Steam is turned into the lower jacketed body and cold water 
through the condenser. After allowing a few minutes to become 
warm, the dome is revolved at a rate of from 1500 to 1800 R. P. M. 
by any suitable power, and as the solvent carrying the bitumen 
is thrown out into the receiving pan, it is volatilized and passes into 




Fig. 42. 

the reflux condenser, falling back into the reservoir on the cover. 
When about 250 cc. has accumulated, it is automatically syphoned 
back into the dome upon the sample as fresh solvent. 

As but three minutes are required to swing the sample dry, 
it is not necessary to revolve the dome continuously; stop it after 
this period of time and do not start again until the gauge glass on 
the reservoir indicates that a fresh portion of solvent has Dassed 
over upon the sample. 

About four treatments are sufficient for a kilogram sample, 
after which the flow of steam is discontinued and cold water re- 
versed through the jacket to hasten cooling. 



580 THE MODERN ASPHALT PAVEMENT. 

The bitumen free from all but minute traces of the finest portion 
of the mineral aggregate, which may be disregarded, will be found 
in the pan, while the clean aggregate is allowed to dry spontane- 
ously and then weighed, the bitumen being determined by dif- 
ference. It is examined further as desired, by sifting, etc., as 
previously described. 

The entire extraction may thus readily be completed in less 
than an hour, with little loss of solvent. 

In handling asphalt block mixtures employing 300 grams of 
sample and but three portions of cold carbon disulphide, an ex- 
traction may be made in about twenty minutes. In the latter 
case, the solvent is recovered in a separate distilling apparatus 
arranged to receive the pan holding the extract directly, or an 
accumulation is worked over at convenient times. 

Density and Voids in Surface Mixtures. — The density which 
a surface mixture can attain on compaction is often a source of 
information as to its quality, and from this the voids in the com- 
pacted material can be calculated. The mixture is compressed 
in a mould made for the purpose. This should consist of a base 
8 inches long, 5 inches wide and 3| inches high. On top of this 
base are found a cylindrical boss or post lj inches in diameter 
and 1 inch high, and a hole of the same or a little larger diameter, 
opening into a hollow in the base. A hollow cylindrical mould 
or sleeve of steel of the same internal diameter as the boss and 
3J inches high is provided and a solid plunger of steel to fit this 

accurately. About grams of the surface mixture is heated 

in a deep iron dish to 325° F., the cylinder and plunger being also 
heated. The cylinder is placed over the post and filled with the 
hot mixture and compressed with the plunger and sharp blows of 
a heavy hammer, or better in any suitable press such as the 
Riehle or Olsen tensile and crushing power machines. When 
ultimate compression has been attained in this way the cylindrical 
mould is removed from the boss and turned over or reversed and 
again placed on the boss. The space formerly occupied by the boss 
now gives an opportunity for the insertion of the plunger and 
compression of the cylinder of asphalt mixture from the other 



METHODS OF ANALYSIS. 581 

end. Finally, the mould is placed over the opening in the base 
and the cylinder of surface knocked out with a few blows of the 
plunger. It should be between 1 and 2 inches long. 

Its density can be determined by weighing it in air and water, 
but the quickest way is to measure its length with calipers to .01 
inch and find its volume in cubic centimeters by reference to the 
table on page 582. 

The weight of the cylinder divided by the volume gives the 
density. This should not fall below 2.20 for good mixtures, made 
with quartz sand. The voids in such a cylinder can be calculated 
from the known proportions and density of the materials of which 
it is composed, as can be seen from the following example : 

The customary surface mixtures consist, in parts by weight, of: 

Sand 75% 

Dust. 10 

Trinidad asphalt cement 15 

100% 

By volume this would be, the density of the sand being 2.65, that 
of dust 2.60, and that of the asphalt cement 1.25: 

Sand 75/2 65... 28.30 or 64.10 

Dust 10/2.60... 3.85 " 8.72 

Asphalt cement. .15/1.25... 12.00 " 27.18 

44.15 100 00 

The cement in use, being 27. 18% of the entire volume of the mix- 
ture, will fill the voids which ordinarily exist in the mineral aggregate 
if the mixture receives its ultimate compression and density. If 
the voids are larger it will be too little and some voids will remain 
unfilled; if they are smaller it will be too much and will make the 
surface too yielding. 

Considering the proportions given as being theoretically cor- 
rect, the density of the resulting mixture, when it receives its 
ultimate compression, should be: 

64.1 vols, at 2.65 density 1 .699 

8.7 " "2.60 " 226 

27.2 " " 1.25 " 340 

100.0 2.265 



582 



THE MODERN ASPHALT PAVEMENT. 



TABLE FOR DETERMINING CONTENTS IN CUBIC CENTIMETERS 
OF CYLINDERS 1.25 INCHES IN DIAMETER AND VARIOUS 
HEIGHTS IN INCHES. 



Height, 


Cubic 


Cubic 


Height, 


Cubic 


Cubic 


Inches. 


Inches. 


Centimeters. 


Inches. 


Inches. 


Centimeters. 


.95 


1.17 


18.17 


1.48 


1.81 


29.66 


.96 


1.18 


19.34 


1.49 


1.83 


29.99 


.97 


1.19 


19.50 


1.50 


1.84 


30.15 


.98 


1.20 


19.66 


1.51 


1.85 


30.32 


.99 


1.22 


19.99 


1.52 


1.86 


30.48 


1.00 


1.23 


20.16 


1.53 


1.87 


30.64 


1.01 


1.24 


20.32 


1.54 


1.89 


30.97 


1.02 


1.25 


20.48 


1.55 


1.90 


31.14 


1.03 


1.26 


20.65 


1.56 


1.91 


31.30 


1.04 


1.28 


20.98 


1.57 


1.93 


31.63 


1.05 


1.29 


21.14 


1.58 


1.94 


31.79 


1.06 


1.30 


21.30 


1.59 


1.95 


31.95 


1.07 


1.31 


21.47 


1.60 


1.96 


32.12 


1.08 


1.33 


21.79 


1.61 


1.98 


32.45 


1.09 


1.34 


21.96 


1.62 


1.99 


32.61 


1.10 


1.35 


22.12 


1.63 


2.00 


32.77 


1.11 


1.36 


22.28 


1.64 


2.01 


32.94 


1.12 


1.37 


22.45 


1.65 


2.02 


33.09 


1.13 


1.39 


22.78 


1.66 


2.04 


33.42 


1.14 


1.40 


22.94 


1.67 


2.05 


33.59 


1.15 


1.41 


23.11 


1.68 


2.06 


33.76 


1.16 


1.42 


23.27 


1.69 


2.07 


33.92 


1.17 


1.44 


23 . 60 


1.70 


2.09 


34.25 


1.18 


1.45 


23.76 


1.71 


2.10 


34.41 


1.19 


1.46 


23.92 


1.72 


2.11 


34.58 


1.20 


1.47 


24.08 


1.73 


2.12 


34.74 


1.21 


1.48 


24.25 


1.74 


2.14 


35.07 


1.22 


1.50 


24.58 


1.75 


2.15 


35.23 


1.23 


1.51 


24.74 


1.76 


2.16 


35.40 


1.24 


1.52 


24.91 


1.77 


2.17 


35.56 


1.25 


1.53 


25.07 


1.78 


2.19 


35.89 


1.26 


1.55 


25.40 


1.79 


2.20 


36.05 


1.27 


1.56 


25.56 


1.80 


2.21 


36.21 


1.28 


1.57 


25.73 


1.81 


2.22 


36.38 


1.29 


1.58 


25.89 


1.82 


2.23 


36.54 


1.30 


1.60 


26.22 


1.83 


2.25 


36.87 


1.31 


1.61 


26.38 


1.84 


2.26 


37.03 


1.32 


1.62 


26.55 


1.85 


2.27 


37 20 


1.33 


1.63 


26.71 


1.86 


2.28 


37.36 


1.34 


1.65 


27.04 


1.87 


2.29 


37.53 


1.35 


1.66 


27.20 


1.88 


2.31 


37.85 


1.36 


1.67 


27.35 


1.89 


2.32 


38.02 


1.37 


1.68 


27.53 


1.90 


2.33 


38.18 


1.38 


1.69 


27.69 


1.91 


2.34 


38.35 


1.39 


1.70 


27.86 


1.92 


2.36 


38.67 


1.40 


1.72 


28.18 


1.93 


2.37 


38.84 


1.41 


1.73 


28.35 


1.94 


2.38 


39.00 


1.42 


1.74 


28.51 


1.95 


2.39 


39.16 


1.43 


1.75 


28.68 


1.96 


2.41 


39.49 


1.44 


1.77 


29.00 


1.97 


2.42 


39.66 


1.45 


1.78 


29.17 


1.98 


2.43 


39.82 


1.46 


1.79 


29.33 


\ 1.99 


2.44 


39.98 


1.47 


1.80 


29.50 


1 2.00 


2.45 


40.15 



METHODS OF ANALYSIS. 583 

The density of the compacted mixture is usually found to be not 
over 2.22, and at this figure there would be about 2 per cent of 
voids. At a density of 2.18 the voids would reach 3.7 per cent. 

The density of coarse mixtures, such as asphalt blocks or as- 
phaltic concrete, may be determined by compressing the hot 
mixture in a mold of appropriate size under suitable pressure in a 
power press. 

Asphalt blocks are weighed as received, first in air and then 
in water, in the most convenient manner, and the density cal- 
culated from the data thus obtained. 

The specific gravity of the mineral aggregate in such mixtures 
is most conveniently determined in a Jackson's apparatus, pre- 
viously referred to. 

Water Absorption of Surface Mixtures. — Cylinders prepared as 
previously described, or, if such a mould is not at hand, compressed 
to the best possible extent in an ordinary diamond mortar, are 
weighed in air and then suspended by a horsehair and immersed 
in distilled water at ordinary temperature and again weighed, while 
still immersed in water and suspended by the hair in the same 
way, at intervals of 1, 2, 7, 15 days and one month. The gain in 
weight shows the water absorbed, which is calculated to milligrams 
per square centimeter, or inch, or pounds per square yard, as may 
be desired, by determining from its dimensions the number of 
square inches of surface the cylinder has. 

Where cylinders are of such density that the surface is but slightly 
acted upon by water and there is no disintegration, they may be 
carefully wiped off and weighed directly. 

An example of the amount of water absorbed by a good mix- 
ture is seen in the following determinations: 



584 



THE MODERN ASPHALT PAVEMENT. 



GAIN IN GRAMS PER SQUARE INCH AND POUNDS PER SQUARE 
YARD OF TRINIDAD SURFACE MIXTURE FROM THE LONG 
ISLAND CITY PLANT OF THE BARBER ASPHALT PAVING 
COMPANY. 

Height of cylinder 1.15 inches 

Diameter 1 . 25 " 

Surface 6 . 97 square inches 



Interval 

After 

Immersion. 


Mgs. Per Square Inch. 


Pounds Per 
Square Yard. 


Gain in 
Interval. 


Total 
Gain. 


Total 
Gain. 


24 hours 
48 " 

7 days 
15 " 
28 " 


.0169 

.0021 
.0092 
.0045 
.0935 


.0190 
.0282 
.0327 
.0362 


.0540 
.0803 
.0930 

. 1031 * 



1 See also pages 465 and 468. 

TABLE FOR DETERMINING SQUARE INCHES OF SURFACE IN 
CYLINDERS 1.25 INCHES IN DIAMETER AND VARIOUS 
HEIGHTS IN INCHES. 



Height. 


Square 
Inches. 


Height. 


Square 
Inches. 


Height. 


Square 
Inches. 


1.00 


6.38 


1.28 


7.48 


1.65 


8.93 


1.10 


6.77 


1.30 


7.56 


1.68 


9.05 


1.11 


6.81 


1.33 


7.68 


1.70 


9.13 


1.12 


6.85 


1.35 


7.76 


1.73 


9.25 


1.13 


6.89 


1.38 


7.87 


1.75 


9.33 


1.14 


6.93 


1.40 


7.95 


1.78 


9.45 


1.15 


6.97 


1.43 


8.07 


1.80 


9.52 


1.16 


7.01 


1.45 


8.15 


1.83 


9.64 


- 1.17 


7.05 


1.48 


8.27 


1.85 


9.72 


1.18 


7.08 


1.50 


8.34 


1.88 


9.84 


1.19 


7.13 


1.53 


8.46 


1.90 


9.92 


1.20 


7.17 


1.55 


8.54 


1.93 


10.03 


1.21 


7.21 


1.58 


8.66 


1.95 


10.11 


1.22 


7.24 . 


1.60 


8.74 


1.98 


10.23 


1.25 


7.36 


1.63 


8.86 


2.00 


10.31 



Weight of water in pounds 
Surface of cylinder in square inches 



X 2.85 = pounds absorbed per square yard. 



METHODS OF ANALYSIS. 585 

Other Physical Tests. — Other physical tests of surface mixtures 
are made at times, such as determination of tensile and compression 
strength, shearing tests, ductility of cements at various tempera- 
tures, abrasion, etc., but as they are only done for special purposes 
they need not be described here. It may be said, however, that 
it should be possible to rub together wet cylinders of any mixture 
without detaching particles of the mineral aggregate, and that if 
this cannot be done such a mixture will not be capable of with- 
standing cold, wet weather. 

Old Street Surfaces. — Old street surfaces are frequently examined 
to determine their composition, the percentage of bitumen and 
the grading of the mineral aggregate, the consistency of the bitumen 
they contain, their density and their power to resist water. All 
these determinations are made according to methods already 
described with almost no modifications except that the material 
should be carefully dried. Enough surface mixture is extracted 
alongside a standard check cement to furnish the same amount 
of bitumen, a piece of surface is shaped to such a form for 
the water absorption test that its superficial area can be calcula- 
ted and the nature of the aggregate, sand and filler, may be as 
carefully examined as a new mixture made with known materials. 

Determination of the Consistency of the Bitumen in Paving 
Mixtures. — Where no sample of the asphalt cement which has 
been used in making a surface mixture is available for the determina- 
tion of its consistency this can be arrived at very closely by proceed- 
ing as directed for the preparation of pure bitumen on page 547. 

Modification of Methods. — The preceding methods are such as 
are in use in the paving industry at the present time; but they 
are, of course, subject to change and improvement from time to 
time. 

Impact Tests for Toughness of Asphalt Surface Mixture. — This 
test is made with the machine devised for the purpose of testing the 
toughness of rocks by Mr. Logan Waller Page, of the Office of Public 
Roads, U.S. Department of Agriculture, and described in Bulletin No. 
79, Bureau of Chemistry, U. S. Department of Agriculture, page 
33, on cylinders 1J inches in diameter and 1 inch high and weighing 
about 50 grams. The cylinders are prepared by compressing 



586 THE MODERN ASPHALT PAVEMENT. 

sufficient of the hot surface mixture, at an appropriate tempera- 
ture, in the steel mould previously described for the preparation 
of test pieces for density. In this way a density of the cylinder 
from 2.2 to 2.3 can readily be attained. When the cylinders are 
cooled they are brought to a normal temperature of 40, 78, and 
100° F., and tested to the breaking point in the machine, that 
mixture being, of course, the toughest which withstands the most 
blows. 

Mr. Page describes the manner of making the test as follows: 
"This test is made on cylinders with an impact machine 
especially designed for the purpose. Instead of a flat end plunger 
resting on the test-piece as in the cementation test, a plunger 
with the lower and bearing surface of spherical shape, having 
a radius of 1 cm. (0.4 inch) is used. It can be seen that the blow 
as delivered through a spherical-end plunger approximates as 
nearly as practicable the blows of traffic. Besides this, it has 
the further advantage of not requiring great exactness in getting 
the two bearing surfaces of the test-piece parallel, as the entire 
load is applied at one point on the upper surface. The test-piece 
is adjusted so that the center of its upper surface is tangent to 
the spherical end of the plunger, and the plunger is pressed firmly 
upon the test-piece by two spiral springs which surround the 
plunger guide-rods. The test-piece is held to the base of the 
machine by a device which prevents its rebounding when a blow 
is struck by the hammer. The hammer weighs 2 kg. and is raised 
by a sprocket chain and released automatically by a concentric- 
electromagnet. The test consists of a 1 cm. fall of the hammer 
for the first blow, and an increase fall of 1 cm. for each succeed- 
ing blow until failure of the test-piece occurs. The number of 
blows required to destroy the test-piece is used to represent the 
toughness." 

Indentification of Bitumens. — It is often necessary to identify 
the source of a solid bitumen or of a flux, or of a mixture of two 
or more of these. In order to accomplish this a complete deter- 
mination of the physical characteristics and proximate chemical 
composition of the bitumen should be first carried out. If the 
data thus obtained are not such as to identify the material, espe- 



METHODS OF ANALYSIS. 587 

cially in the case of asphalt cements, an examination of the character 
of the mineral matter that is present may assist in forming an 
opinion in regard to the origin of the solid bitumen that is present, 
the ash being more or less characteristic of the source from which 
the bitumen is derived. For example, the ash in Trinidad asphalt 
is characterized by a light pink color and, on microscopic exami- 
nation, is found to contain very sharp particles of quartz with 
fine clay colored by the oxide of iron which is present. If an ash 
of this description is not detected it will be safe to say that the 
material contains no Trinidad asphalt. Some Cuban asphalts 
have a somewhat similar ash, but confusion cannot arise if they 
are compared microscopically with one obtained from a known 
sample of Trinidad asphalt. 

If the extremely fine mineral matter which remains in suspen- 
sion in carbon disulphide, which is obtained in a correction in 
the course of analysis, is examined, this will also be found to be 
characteristic. 

If the bitumen under examination contains but a small per- 
centage of ash and this consists of not excessively fine mineral 
particles, it may be assumed that a solid native bitumen is present 
and that the material is not composed entirely of a residual pitch. 
The residual pitches yield but traces of mineral matter and this 
is extremely fine, usually ferruginous, and derived from the stills 
in which the distillation has been carried on. 

Gilsonite is so extremely pure that its mineral matter can only 
be differentiated from that of residual pitch from the fact that it 
is not so red in color. 

The fixed carbon which the bitumen yields on ignition is a very 
important factor in fixing its origin. A very high percentage 
points to a grahamite. The residual pitch from Texas oil yields 
more fixed carbon than those from California oils. The asphalts, 
generally, yield from 10 to 15 per cent of fixed carbon. The fixed 
carbon yielded by asphalt cements may be compared with that of 
cements of known origin. 

The proportion of the bitumen soluble in 88° naphtha which is 
attacked by sulphuric acid, according to the method which has 
been described, will differentiate bitumens such as gilsonite and 



588 THE MODERN ASPHALT PAVEMENT. 

mixtures containing large proportions of it from those made with 
asphalts. The same determination will differentiate the California 
fluxes from those made from Texas oil, although this may be gen- 
erally arrived at from the difference of the specific gravity of the 
two materials and by the fact that the Texas oil contains about 
one per cent of parafnne scale. 

Other determinations which have been made in the course 
of the general analysis will have their value in special cases, and the 
methods may be applied according to the judgment of the analyst. 

It may be noted that none of the true asphalts contain bitumen 
insoluble in cold carbon tetrachloride which is soluble in carbon 
disulphide. 



CHAPTER XXIX. 



SOLVENTS. 



Bitumen, as has appeared in the preceding pages, is entirely 
or partially dissolved by very many solvents, and the relative 
solubility in the different ones has been used as a means of differ- 
entiating them. Analysts are not, however, agreed as to the most 
suitable solvents to use for this purpose. 

For the determination of total bitumen bisulphide of carbon is 
generally employed, but chloroform and oil of turpentine have also 
been used for this purpose. One analyst uses naphtha of 74° 
B., boiling between 40° and 60° C, another both 88° and 62° B. 
naphtha; while others have used acetone and ethyl ether as solvent 
for the malthenes. It is of interest to determine what there is in 
favor of the different solvents and what there is against them. 

Chloroform. — Chloroform is a most excellent solvent for bitu- 
men and might, perhaps, be used for making the determination 
of total bitumen were it not for certain disadvantages. In a pure 
form it is extremely expensive, costing $1.00 per pound. Commer- 
cial chloroform is not sufficiently pure to be used as a solvent, as 
can be seen from the following determinations: 

BOILING-POINT. 





Temperature. 


Per Cent Distillate. 


Pure chloroform 


61.2° C. 

55° to 60° C. 

60° "62° C. 

Residue 




f 


5.7% 
92 9 


Commercial chloroform \ 


1 


1 4 








100.0 



589 



590 THE MODERN ASPHALT PAVEMENT. 

From these figures it is evident that the commercial chloro- 
form contains at least 10 per cent of impurities, the amount of 
which is not constant, and it is, therefore, not suitable for use as a 
solvent for bitumen. Chloroform possesses the additional disad- 
vantage of evaporating much moreslowlythanbisulphide of carbon; 
and, as it is non-inflammable, it cannot be burned off rapidly 
in determining the correction for the mineral matter, as is the case 
with bisulphide of carbon. For these reasons it is not probable 
that it will ever be adopted as a standard solvent. 

Oil of Turpentine. — Oil of turpentine is not a definite compound. 
It boils between 97° and 160° C, the greater portion passing over 
between 155° and 160° C. It is an artificial product, having no 
constant composition, and is, therefore, unsuitable for use as a stand- 
ard solvent. 

Bisulphide of Carbon. — Bisulphide of carbon for many reasons is 
the best solvent for the determination of total bitumen. Objec- 
tion has been raised against it because a slight amount of bitumen, 
which is dissolved by chloroform and turpentine, is not soluble 
in it, but for technical work at least it is entirely satisfactory. 
It possesses the great advantage that, if redistilled, it is very pure, 
with a constant boiling-point of 46° C. and specific gravity 1.27. 
It is the cheapest solvent for total bitumen thit is available, as it 
can be brought in thousand-pound lots at six cents per pound or 
practically free from sulphur at 8 cents, and it has not been found 
necessary for ordinary bitumen determinations to redistil this 
material. It will undoubtedly be adopted as the standard solvent 
for the purpose for which it is used. 

Carbon Tetrachloride. — For the asphalts and some of the 
native bitumens carbon tetrachloride may be substituted for 
bisulpide of carbon; but, as has appeared in previous pages, in cer- 
tain cases it does not dissolve all the bitumen which is soluble 
in the latter solvent. On this account it is never used for the 
determination of total bitumen, but only to discover the percent- 
age of bitumen which is soluble in bisulphide of carbon, which it 
does not dissolve, as a means of differentiating the amount of 
material which has been injured by natural weathering or over- 
heating, for which purpose it is extremely useful. The specific 
gravity of the pure carbon tetrachloride is 1.604 at 15° C, but the 



SOLVENTS. 



591 



commercial supply often contains sufficient bisulphide of carbon 
to lower this. Bisulphide of carbon can be largely removed by 
blowing a current of air through the solvent or by distilling it with 
a Young dephlegmator 1 until the boiling-point leaches 76.6° C. 
The best carbon tetrachloride found on the market was that fur- 
nished by the Acker Process Company, Niagara Falls, N. Y. This 
had a density of 1.604, whereas inferior supplies may fall as low 
as 1,593. This concern has, however, gone out of business, and 
the less pure and more expensive German product must now be 
used after redistillation. 

Ethyl Ether. — No objection can be raised to the use of ether 
for the determination of malthenes if the purest product made by 
Squibb is used. The cost of this is, however, prohibitive in a labo- 
ratory where any large amount of work is carried on. Commercial 
ether is too impure and too irregular in composition to be used 
for the purpose; it contains alcohol and water. The use of ether 
as a solvent must, therefore, be abandoned. 

Acetone. — The acetone found on the market under the designa- 
tion "chemically pure" is of fairly constant boiling-point ; that of 
the pure material being 56.5° C. 

BOILING-POINT. 



Temperature. 


Per Cent Distillate. 


56° to 57° C. 
57° " 58° C. 
58° " 59° C. 
59° / ' 60° C. 
Residue 


26.6% 
58.4 

9.0 

4.0 

2.0 


100.0 

- 



This solvent is, like ether, very expensive, 50 cents per pound, 
and its general use is prohibited by this fact. 

Commercial acetone, costing $1.75 per gallon, is quite unsuitable 
for use as a solvent owing to its lack of purity and uniformity. A 



1 J. Chem. Soc, 1899, 75, II, 



592 



THE MODERN ASPHALT PAVEMENT. 



specimen distilled in the author's laboratory gave the following 
fractions : 

BOILING-POINT. 



Temperature. 


Per Cent Distillate. 


56.8° to 57° C. 


2.9% 


57° to 58° C. 


13.7 


58° ' ' 59° C. 


32.2 


59° ' ' 60° C. 


15.4 


60° " 61° C. 


9.1 


61° " 62° C. 


4.8 


62° ' ' 63° C. 


4.8 


63° " 64° C. 


2.9 


64° ' ' 65° C. 


2.4 


65° " 70° C. 


4.3 


70° " 75° C. 


3.3 


75° " 80° C. 


2.2 


Residue 


2.0 


100.0 



It is evident that the commercial material consists largely 
of substances boiling at higher temperature than pure acetone. It 
will, for the reasons given, never be used as a standard solvent. 

Light Petroleum Distillates. — Light petroleum distillates have 
been very generally used for the separation of the softer constitu- 
ents of the solid bitumens, but different analysts have used it of 
various boiling-points and densities. None of these solvents con- 
sists, of course, of any one hydrocarbon; they are mixtures chiefly 
of isopentane, pentane, isohexane, hexane, isoheptane, heptane and 
the octanes in 62° naphtha, together with small percentages of other 
hydrocarbons such as methylene, pentamethylene and hexamethy- 
lene, but the amounts of the latter are too small to have any bearing 
upon the solvent power. The boiling points of the principal con- 
stituents of the naphthas are, according to Young: 1 



1 J. Chem. Soc, 1898, 73, II, 906. 



SOLVENTS. 
BOILING-POINTS. 



593 



Name. 


760 Milli- 
meters. 


Isopentane „ 


28° C. 

36° C. 

50° C. 

61° C. 

69° C. 

72° C. 

80° C. 

81° C. 

90° C. 

98° C. 
102° C. 
111° C. 
125° C. 


Pentane 


Pentamethylene 


Isohexane 


Hexane 


Methylpentamethylene 


Benzene 


Hexamethylene . 


Isoheptane 


Heptane 


Methylhexam ethylene. „ 


Toluene 


Octane 





On fractioning a naphtha of 88° Beaume density with a Young 
dephlegmator of eighteen sections the following results were ob- 
tained : 

BOILING-POINT. 



Temperature. 


Per Cent of 
Distillate. 


Specific Gravity 
20° C/20° C. 


25° to 30° C. 


21.5% 


.6287 


30° " 35° C. 


8.8 


.6324 


35° " 40° C. 


12.7 


.6287 


40° ' ' 45° C. 


13.6 


.6317 


45° " 50° C. 


11.2 


.6448 


50° " 55° C. 


5.6 


.6589 


55° ' ' 60° C. 


4.8 


.6539 


60° " 65° C. 


.8.8 


.6566 


65° ' ' 70° C. 


3.2 


.6673 


Residue 


9.8 


.7027 


100.0 



It is evident from the above figures that this naphtha is far from 
being composed of a single hydrocarbon. It contains a preponder- 
ance of iso- and normal pentanes and isohexane, but it would require 
a very large number of fractionations 1 with the most perfect form 



See Young, " Fractional Distillation," Macmillan & Co., 1903. 



594 THE MODERN ASPHALT PAVEMENT. 

of dephlegmator to obtain a single hyrdocarbon or even a mixture 
of pentanes. One distillation, with no definite specifications of the 
method, would have little or no effect; and, in practice, it has not 
been found to result in any improvement of the naphtha as a sol- 
vent commensurate with the trouble involved. The same is the 
case with 74° and 62° Beaume naphtha. The least dense of these 
naphthas consists of a mixture of hydrocarbons, the most prominent 
of which are the hexanes, the more dense one containing heptanes 
and octanes. The author, therefore, considers it necessary to 
merely see that the density of every lot of naphtha in use should be 
a standard one, such as .7290 for 62° Beaume, .6863 for 74° Beaume, 
and .6422 for 88° Beaume. If the lot in hand is denser than the 
standard it must be rejected, but if it is lighter it can be brought 
to the standard, in the case of the 88° Beaume solvent, by blowing 
with a current of air for a short time, or in the heavier ones by 
distillation. The solvent power in this way will be found to be 
quite as uniform among different lots as if a single fractionation 
was attempted. 

It remains to determine whether there is a preference for one 
density of naphtha over another. If one alone is to be used that 
of 74° Beaume may be well accepted as being a solvent of medium 
power, but the author has found that the use of both. 88° and 62° 
Beaume naphtha is most desirable, as in this way a more thorough 
differentiation can be accomplished. 1 

From the preceding data it would seem that the desirable 
solvents for use in the asphalt-paving industry are those which 
have been mentioned in the chapter on Methods of Analysis; 
bisulphide of carbon for the total bitumen, carbon tetrachloride for 
the detection of bitumen which has been affected by overheating or 
weathering, and 88° and 62° Beaume naphtha for the purpose of 
determining whether a bitumen shows a normal relation between 
the amounts dissolved by these two solvents or points to the addi- 
tion of a flux to an extremely hard asphalt. 

1 See page 542. 



CHAPTER XXX. 

EQUIPMENT OF A LABORATORY FOR CONTROL OF 
ASPHALT WORK. 

For making the necessary determinations for the control of 
the materials and mixtures in use in the construction of an asphalt 
pavement, according to the methods which have been outlined in 
a previous chapter, no elaborate laboratory is necessary. Sub- 
laboratories for this purpose have been established economically by 
the author at many plants under his control. 

The room which is to be used need not be large, but should be 
well lighted. It should contain several tables securely fastened 
to the wall. That upon which the balance and penetration 
machine are to be placed should be as free from vibration as 
possible. 

The equipment usually supplied for such a laboratory consists 
of the following pieces of apparatus: 

1 Chaslyn balance $15 00 

2 Bunsen burners, No. 2597, Eimer & Amend, 

New York 2 00 

1 Fairbanks sand scale, No. 485, Fairbanks Co., 

New York 6 00 

1 set of sieves (200, 100, 80, 50, 40, 30, 20, 10 

mesh) 15 75 

1 New York Testing Laboratory Penetrometer, 

Howard & Morse, 1197 DeKalb Avenue, Brook- 
lyn, N. Y 60 00 

2 thermometers for penetrometer, C. J. Tagliabue 

Co., N. Y 2 50 

595 



m THE MODERN ASPHALT PAVEMENT. 

1 doz. 2J" glass funnels, E. & A. No. 3345 1 20 

1 doz. watch glasses to cover funnels, E. & A. No. 

7189 , 56 

1 doz. Erlenmeyer flasks, Jena glass, 200 cc, E, 

& A. No. 3863 1 68 

§ doz. 4J" porcelain evaporating dishes, E. & A. 

No. 2963 2 70 

J doz. watch glasses to cover dishes, E. & A. No. 

7189 75 

J doz. Royal Berlin porcelain crucibles, No. 0, with- 
out covers, E. & A. No. 2850 1 38 

4 Royal Berlin porcelain crucibles No. 2, 

without covers, E. & A. No. 2850 1 40 

4 packages filter paper, S. & S. No. 597, E. & A. 

No. 3213 (3i") 1 00 

1 glass cylinder, graduated to 100 cc, E. & A. No. 

2919 70 

J doz. flat bottom sample tubes, 4" high by f" 

diameter, E. & A. No. 4647 30 

1 pair tongs, E. & A. No. 2883-B 85 

2 iron ring stands, E. & A. No. 4812 1 30 

2 iron sand baths, 6" deep form, E. & A. No. 4555 44 

1 spatula, 4", E. & A. No. 4643 25 

1 spatula, 6", E. & A. No. 4643 35 

1 spatula, 8", E. & A. No. 4643 55 

3 clay triangles, small, to fit R. B. crucibles, No. 

0, E. & A. No. 4965 25 

3 clay triangles, large, to support porcelain 

evaporating dishes, E. & A. No. 4965 25 

1 brass mold for flow test K 1 25 

3 brass flow plates 1 1 65 

1 New York Testing Laboratory-Seebach drying 

oven (Hauck-Seebach Co., 291 Essex Street, 

Brooklyn, New York.) , 25 00 

1 doz. crystallizing dishes, straight sides, 2|" 

diameter, E. & A. No. 2960 1 68 

1 New York Testing Laboratory, Maurer, N. J. 



EQUIPxMENT OF A LABORATORY. 597 

2 chemical thermometers, 50-600° F., gas filled, 

style No. 4881 $5 00 

J doz. camel's hair brushes, large size, E. & A. No. 

2943 18 

1 New York State Board of Health oil tester with 

Bunsen burner, E. & A. No. 4160 8 00 

J doz. beakers, 600 cc, 115 mm. high and 85 mm. 

diameter, E. & A. No. 3872 1 80 

1 foot blower, small, E. & A. No. 2308 4 00 

\ pound glass tubing, T V' diameter 15 

\ " glass rod, \" diameter 15 

1 washing bottle, 1 quart, E. & A. No. 7181 75 

50 pounds carbon disulphide, at 10 cents 5 00 

5 gallons 88° naphtha, at 20 cents 1 00 

1 piece rubber tubing, T y, E. & A. No. 4540 2 00 

1 gross 2-oz. flat tin boxes, E. & A. No. 2482 1 38 



$176 15 



The prices given are list, and an estimate should be requested 
before placing an order, as discounts are given. 

The use of the above apparatus has been described in 
the methods. The Primus burner is the most convenient 
one at points where gas is not available, as it burns kerosene 
and is kept clean more easily than the Barthel burner, which burns 
benzine, 62° Beaume naphtha. 

With the preceding outfit in the hands of a clever yard-foreman 
or assistant a contractor or a city official should be able, following 
the methods which have been described, to control accurately the 
work under his direction. 



APPENDIX. 



As a type of modern asphalt paving specifications, those of 
Kansas City, Mo., for 1907, are appended for the information of 
the reader. As this book goes to press modified specifications are 
in course of preparation in Kansas City, Mo. 



BINDER COURSE. 

Upon the base of cement concrete there shall be laid a binder course 
of asphaltic concrete which, when ultimately compressed by rolling, shall 
have an average thickness of . . ( ) inches, and shall be com- 
posed and laid as follows: The Binder Course shall consist principally of 
clean broken stone, which shall pass through a one (1) inch screen. To this 
stone shall be added well graded sand, or reduced old asphaltic surface 
mixture (which consists principally of sand) in a sufficient quantity to fill 
the voids between the stone when laid in mass. The old Asphaltic Surface 
mixture used in the binder course before being used shall be reduced by 
being thoroughly disintegrated. To the materials just described shall be 
added a sufficient quantity of asphaltic cement to thoroughly coat each 
particle of the composition. 

The Asphaltic Cement to be used in the Binder Course shall be composed 
of a refined asphalt fluxed with a heavy petroleum oil or liquid asphalt. 
This asphaltic cement shall be composed of such materials as will fulfill the 
chemical and physical tests required of the asphaltic cement for the Asphalt 
Wearing Surface. 

These component materials shall be combined and mixed while hot by 
machinery in such proportions that the percentage of bitumen in the binder 
when laid shall approximately be from 3 per cent to 6 per cent by weight 
of the total mixture, and such that the aggregate mass shall, when laid and 
rolled, form a dense compact asphaltic concrete suitable and capable of 
sustaining an asphalt wearing surface without vibration. The mixture 
thus prepared shall be spread upon the street base with rakes while in a hot 
plastic condition, and shall be rammed and rolled until it forms a compact 

599 



600 THE MODERN ASPHALT PAVEMENT. 

and thoroughly bonded binder course of the required thickness, and its top 
surface shall be approximately parallel with the completed surface of the 
pavement. 

The binder course shall not be laid upon the concrete base until the 
expiration of at least ten (10) days in case Natural Cement Concrete is 
used, or until the expiration of at least five (5) days in case Portland Cement 
Concrete is used, and then only when the Engineer is satisfied that the con- 
crete has set sufficiently hard to bear the weight of a ten ton roller. 
fv' The surface of the concrete foundation shall be swept clean and shall 
be dry during the laying of the binder, which shall not come in contact with 
moist or frozen surfaces. No traffic on the binder of horses or vehicles is 
to take place except such as is required to lay the asphalt pavement surface 
layer thereon. The traffic then necessary shall in no way injure the Binder. 
The surface of the Binder must be kept clean at all times and in perfect 
condition, so as to facilitate the adhesion of the asphalt pavement when 
laid upon it. 

ASPHALT WEARING SURFACE. 

The wearing surface shall be laid upon the binder course and, when 

thoroughly compressed, shall have an average thickness of ( ) 

inches. The wearing surface shall consist of a uniform mixture of asphaltic 
cement, sand and a mineral filler, but the asphaltic cement and mineral 
filler may be used without separation and in their natural state of com- 
bination or mixture. 

The asphaltic cement, when considered apart from the mineral matter, 
shall have the following characteristics: 

It shall be free from water or decomposition products. 

The various hydrocarbons composing it shall be present in homogeneous 
solution, no oily or granular character being present. 

Penetration. — It must, when tested at 77 deg. Fahrenheit, have a 
penetration of from 3 to 9 millimeters when tested for five seconds with a 
No. 2 needle weighted with 100 grams, according to the nature of the asphalt 
and the conditions under which it is employed. It must not be so suscep- 
tible to changes of temperature that if at 32 deg. Fahrenheit it shows a hard- 
ness indicated by 1 millimeter penetration, at 115 deg. Fahrenheit it will 
not be so soft as to give more than 35 millimeters penetration, using the 
above method of testing. 

Twenty (20) grams of it shall not lose more than four (4) per cent in 
weight upon being maintained at a uniform temperature of 325 deg. Fahr- 
enheit for seven (7) hours in a cylindrical vessel two and one-half (2J) 
inches in diameter by two (2) inches high. 

Twenty (20) grams of it shall not lose more than eight and one-half (8£) 
per cent upon being maintained at a uniform temperature of 400 deg. 



APPENDIX. 601 

Fahrenheit for seven (7) hours in a cylindrical vessel two and one-half (2^) 
inches in diameter by two (2) inches high. 

It shall be soluble in chemically pure carbon disulphide at air tempera- 
ture to the extent of at least ninety-five (95) per cent. 

It shall not contain of carbonaceous matter insoluble in chemically pure 
carbon disulphide, air temperature, more than four and one-half (4|) per 
cent. 

It shall be soluble in 87 deg. Beaume petroleum naphtha, air temperature, 
to the extent of not less than sixty-five (65) per cent and not more than 
eighty (80) per cent. 

Its solubility in carbon tetrachloride shall not be more than one and 
one-half (H) per cent less than its solubility in carbon disulphide — both 
tests being made at air temperature. 

It shall show of fixed carbon not more than fifteen (15) per cent. 

It shall show a flashing point (New York State Closed Oil Tester) of 
more than 350 deg. Fahrenheit. 

It shall not contain more than three (3) per cent of parafline scale, the 
Holde method of determining parafhne scale being used. 

Use. — The bitumen entering into the composition shall have been in 
use in the street paving industry under conditions similar to those con- 
templated in this contract, at least four (4) years prior to the letting of this 
contract. The asphaltic cement shall constitute not less than nine and 
one-half (9^), nor more than thirteen (13) per cent of the surface mixture. 

Mixing. — While the ingredients of the asphalt wearing surface^are being 
mixed, and at the time it is being taken from the mixer for use, the paving 
composition must be thoroughly agitated at a temperature of between 
275 deg. and 330 deg. Fahrenheit, and if any part of it settles, it must be 
again thoroughly agitated before being used. 

The characteristics of this material and the tests herein required to be 
complied with are to be met at the time of making and laying the pave- 
ment. It is recognized that its properties change somewhat upon being 
exposed to weather and street traffic. 

The asphaltic cement used under this contract must not be materially 
changed as to the brands, kinds, proportions and qualities of the ingredients 
of the mixture during the progress of the work. 

The materials, the machinery, testing apparatus and the works of the 
Contractor shall at all times between the date of the contract for the work 
and the completion of the work, be open to inspection of the City Engineer 
for the purpose of enabling him to determine whether the requirements of 
these specifications are being complied with. No asphaltic cement injured 
by heating, or otherwise, will be permitted to go into the work. 

Sand. — The sand must be clean and sharp and shall not be of uniform 
size, but various percentages shall pass sieves of the following square mesh 
per linear inch: 200, 100, 80, 50, 40, 30, 20, and 10. 



602 THE MODERN ASPHALT PAVEMENT. 

It shall be present in the surface mixture to such an extent that not less 
than three (3) per cent nor more than eight (8) per cent of such surface 
mixture shall consist of sand passing a 200 mesh sieve ; that not less than 
fifteen (15) per cent nor more than thirty-two (32) per cent shall pass an 
80 and be retained by a 200 mesh sieve; that not less than twenty-five (25) 
per cent nor more than forty-five (45) per cent shall pass a 40 and be 
retained by an 80 mesh sieve; that not less than ten (10) per cent nor 
more than thirty (30) per cent shall pass a 10 and be retained by a 40 mesh 
sieve. 

The mineral particles, including limestone or Portland cement, which 
when thoroughly mixed by air blast, or otherwise, with distilled water at a 
temperature of 77 deg. Fahrenheit, will subside in fifteen (15) seconds, is 
by the terms of this contract regarded as sand. This test shall be conducted 
in a beaker about six (6) inches high and nearly full of the water and mate- 
rial to be tested. 

Filler. — The filler shall be composed of mineral particles so small that 
when they are thoroughly agitated with distilled water at a temperature 
of 77 deg. Fahrenheit, by means of an air blast, or otherwise, they will not 
subside in fifteen (15) seconds, but can be poured off with the water after a 
lapse of fifteen (15) seconds from the time agitation ceased. This test is to 
be carried out in a beaker as described in the preceding paragraph. Such 
fine mineral matter shall be insoluble in water and shall by the terms of 
this contract be known as filler and shall constitute not less than four (4) 
per cent nor more than seven (7) per cent of the total wearing surface. 

The exact proportions of all constituents of the wearing surface to be 
determined by the Contractor shall be subject to the approval of the City 
Engineer. 

The sand and asphaltic cement shall be heated separately to about 330 
deg. Fahrenheit. The mineral filler will be mixed while cold with the sand 
while hot, and which shall have been heated to about 330 deg. Fahrenheit, 
and then this composition shall be mixed with the asphaltic cement at the 
temperature stated, in such a manner and with such apparatus as to effect 
a thoroughly homogeneous mixture. * 

Samples of all material entering into the composition of the pavement 
shall be supplied to the City Engineer, when required, in suitable tin boxes 
and cans, and the Contractor, when required, shall give to the Engineer a 
written statement of the date and geographical source of all crude or other 
materials from which the refined asphaltum is made, and proportions of 
each, also per cent of pure bitumen contained therein. The City Engineer, 
or his representatives, shall have access to all branches of 'the works at any 
time. He, or his representatives, shall inspect the material lurnished and 
work done upon the asphalt pavement, and have power to enforce all require- 
ments of specifications. He shall at all times have access to the works and 
laboratories of the Contractors, and shall have privilege to take samples 



APPENDIX. 603 

from such works, or from material upon the streets, as may be deemed 
advisable or necessary for testing purposes. 

It shall be the duty of the Contractor, when performing work under the 
contract, to furnish complete detailed analyses of the ingredients of the 
paving mixture to the City Engineer, whenever requested by him so to do. 

The paving mixture prepared in the manner thus indicated shall be 
brought to the ground in carts or wagons at a temperature of not less than 
250 deg. nor more than 350 deg. Fahrenheit. If the temperature of the 
air is less than 60 deg. Fahrenheit, the Contractor must provide canvas 
covers for use in transit. It will then be thoroughly spread by means of 
hot rakes in such a manner as to give a uniform and regular grade, so that 
aftei having reached its ultimate compression it shall have a thickness shown 
on the plans and required in the specifications. This depth shall be con- 
stantly tested by means of gauges. The surface shall then be compressed 
by a small steam-roller or hand-roller, after which a small amount of 
Hydraulic Cement will be spread over it, and it will then be thoroughly 
compressed by a steam-roller weighing not less than two hundred and fifty 
(250) pounds to the inch run, the rolling being continued for not less than 
five (5) hours for every thousand square yards of surface. 

Asphaltic Wearing Surface. — The acceptance of said work by the 
City Engineer after its completion, shall be conclusive of the fact that the 
provisions hereof under the above heading, "Asphalt Wearing Surface," 
has been complied with. 

Repairs. — All repairs of asphalt pavement required to be made by the 
Contractor during the guarantee period shall be made with mixtures similar 
and equal to and laid in the manner of those described above. 



604 



THE MODERN ASPHALT PAVEMENT. 



COMPARISON OF ACTUAL SPECIFIC GRAVITY AND DEGREES 
BEAUM& HYDROMETER. 



For liquids lighter than water, specific gravity = 



140 



130 + ° Be 



; at 60° F. 



°B6. 


Sp. Gr. 


°B£. 


Sp. Gr. 


°B£. 


Sp. Gr. 


° B6. 


Sp. Gr. 


10.0 


1.0000 


14.0 


0.9722 


18.0 


0.9459 


22.0 


0.9211 


.1 


0.9993 


.1 


0.9715 


.1 


0.9453 


.1 


0.9204 


.2 


0.9986 


.2 


0.9709 


.2 


0.9447 


.2 


0.9198 


.3 


0.9979 


.3 


0.9702 


.3 


0.9440 


.3 


0.9192 


.4 


0.9972 


.4 


0.9695 


.4 


0.9434 


.4 


0.9186 


.5 


0.9964 


.5 


0.9689 


.5 


0.9428 


.5 


0.9180 


.6 


0.9957 


.6 


0.9682 


.6 


0.9421 


.6 


0.9174 


.7 


0.9950 


.7 


0.9675 


.7 


0.9415 


.7 


0.9168 


.8 


0.9943 


.8 


0.9669 


.8 


0.9409 


.8 


0.9162 


.9 


0.9936 


.9 


0.9662 


.9 


0.9402 


.9 


0.9156 


11.0 


0.9929 


15.0 


0.9655 


19.0 


0.9396 


23.0 


0.9150 


.1 


0.9922 


.1 


0.9649 


.1 


0.9390 


.1 


0.9144 


.2 


0.9915 


.2 


0.9642 


.2 


0.9383 


.2 


0.9138 


.3 


0.9908 


.3 


0.9635 


.3 


0.9377 


.3 


0.9132 


.4 


0.9901 


.4 


0.9629 


.4 


0.9371 


.4 


0.9126 


.5 


0.9894 


.5 


0.9622 


.5 


0.9365 


.5 


0.9121 


.6 


0.9887 


.6 


0.9615 


.6 


0.9358 


• .6 


0.9115 


.7 


0.9880 


.7 


0.9609 


.7 


0.9352 


.7 


0.9109 


.8 


0.9873 


.8 


0.9602 


.8 


0.9346 


.8 


0.9103 


.9 


0.9866 


.9 


0.9596 


.9 


0.9340 


.9 


0.9097 


12.0 


0.9859 


16.0 


0.9589 


20.0 


0.9333 


24.0 


0.9091 


.1 


0.9852 


.1 


0.9582 


.1 


0.9327 


.1 


0.9085 


.2 


0.9845 


.2 


0.9576 


.2 


0.9321 


.2 


0.9079 


.3 


0.9838 


.3 


0.9569 


.3 


0.9315 


.3 


0.9073 


.4 


0.9831 


.4 


0.9563 


.4' 


0.9309 


.4 


0.9067 


.5 


0.9825 


.5 


0.9556 


.5 


0.9302 


.5 


0.9061 


.6 


0.9818 


.6 


0.9550 


.6 


0.9296 


.6 


0.9056 


.7 


0.9811 


.7 


0.9543 


.7 


0.9290 


.7 


0.9050 


.8 


0.9804 


.8 


0.9537 


.8 


0.9284 


.8 


0.9044 


.9 


0.9797 


.9 


0.9530 


.9 


0.9278 


.9 


0.9038 


13.0 


0.9790 


17.0 


0.9524 


21.0 


0.9272 


26.0 


0.9032 


.1 


0.9783 


.1 


0.9517 


.1 


0.9265 


.1 


0.9026 


.2 


0.9777 


.2 


0.9511 


.2 


0.9259 


.2 


0.9021 


.3 


0.9770 


.3 


0.9504 


.3 


0.9253 


.3 


0.9015 


.4 


0.9763 


.4 


0.9498 


.4 


0.9247 


.4 


0.9009 


.5 


0.9756 


.5 


0.9492 


.5 


0.9241 


.5 


0.9003 


.6 


0.9749 


.6 


0.9485 


.6 


0.9235 


.6 


0.8997 


.7 


0.9743 


.7 


0.9479 


.7 


0.9229 


.7 


0.8992 


.8 


0.9736 


.8 


0.9472 


.8 


0.9223 


.8 


0.8986 


. -9 

f 


0.9729 


.9 


0.9466 


.9 


0.9217 


.9 


0.8980 



APPENDIX. 



605 



COMPARISON OF ACTUAL SPECIFIC GRAVITY AND DEGREES 
BEAUME HYDROMETER— Continued. 



•M 


Sp. Gr. 


°B6. 


Sp. Gr. 


°B<5. 


Sp. Gr. 


°B<*. 


Sp. Gr. 


26.0 


0.8974 


31.0 


0.8696 


36.0 


0.8434 


41.0 


0.8187 


1 .1 


0.8969 


.1 


0.8690 


.1 


0.8429 


.1 


0.8182 


.2 


0.8963 


.2 


0.8685 


.2 


0.8424 


.2 


0.8178 


.3 


0.8957 


.3 


0.8679 


.3 


0.8419 


.3 


0.8173 


.4 


0.8951 


.4 


0.8674 


.4 


0.8413 


.4 


0.8168 


.5 


0.8946 


.5 


0.8669 


.5 


0.8408 


.5 


0.8163 


.6 


0.8940 


.6 


0.8663 


.6 


0.8403 


.6 


0.8159 


.7 


0.8934 


.7 


0.8658 


.7 


0.8398 


.7 


0.8154 


.8 


0.8929 


.8 


0.8653 


.8 


0.8393 


.8 


0.8149 


.9 


0.8923 


.9 


0.8647 


.9 


0.8388 


.9 


0.8144 


[27.0 


0.8917 


32.0 


0.8642 


37.0 


0.8383 


42.0 


0.8140 


.1 


0.8912 


.1 


0.8637 


.1 


0.8378 


.1 


0.8135 


.2 


0.8906 


.2 


0.8631 


.2 


0.8373' 


.2 


0.8130 


.3 


0.8900 


.3 


0.8626 


.3 


0.8368 


.3 


0.8125 


.4 


0.8895 


.4 


0.8621 


.4 


0.8363 


.4 


0.8121 


.5 


0.8889 


.5 


0.8615 


.5 


0.8358 


.5 


0.8116 


.6 


0.8883 


.6 


0.8610 


.6 


0.8353 


.6 


0.8111 


.7 


0.8878 


.7 


0.8605 


.7 


0.8348 


.7 


0.8107 


.8 


0.8872 


.8 


0.8600 


.8 


0.8343 


.8 


0.8102 


.9 


0.8866 


.9 


0.8594 


.9 


0.8338 


.9 


0.8097 


28.0 


0.8861 


33.0 


0.8589 


38.0 


0.8333 


43.0 


0.8092 


.1 


0.8855 


.1 


0.8584 


.1 


0.8328 


.1 


0.8088 


.2 


0.8850 


.2 


0.8578 


.2 


0.8323 


.2 


0.8083 


.3 


0.8844 


.3 


0.8573 


.3 


0.8318 


.3 


0.8078 


.4 


0.8838 


.4 


0.8568 


.4 


0.8314 


.4 


0.8074 


.5 


0.8833 


.5 


0.8563 


.5 


0.8309 


.5 


0.8069 


.6 


0.8827 


.6 


0.8557 


.6 


0.8304 


.6 


0.8065 


.7 


0.8822 


.7 


0.8'552 


.7 


0.8299 


.7 


0.8060 


.8 


0.8816 


.8 


0.8547 


.8 


0.8294 


.8 


0.8055 


.9 


0.8811 


.9 


0.8542 


.9 


0.8289 


.9 


0.8051 


29.0 


0.8805 


34.0 


0.8537 


39.0 


0.8284 


44.0 


0.8046 


.1 


0.8799 


.1 


0.8531 


.1 


0.8279 


.1 


0.8041 


.2 


0.8794 


.2 


0.8526 


.2 


0.8274 


.2 


0.8037 


.3 


0.8788 


.3 


0.8521 


.3 


.8269 


.3 


0.8032 


.4 


0.8783 


.4 


0.8516 


.4 


0.8264 


.4 


0.8028 


.5 


0.8777 


.5 


0.8511 


.5 


0.8260 


.5 


0.8023 


.6 


0.8772 


.6 


0.8505 


.6 


0.8255 


.6 


0.8018 


.7 


0.8766 


.7 


0.8500 


.7 


0.8250 


.7 


0.8014 


.8 


0.8761 


.8 


0.8495 


.8 


0.8245 


.8 


0.8009 


.9 


0.8755 


.9 


0.8490 


.9 


0.8240 


.9 


0.8005 


30.0 


0.8750 


35.0 


0.8485 


40.0 


0.8235 


45.0 


0.8000 


.1 


0.8745 


.1 


0.8480 


.1 


0.8230 


.1 


0.7995 


.2 


0.8739 


.2 


0.8475 


.2 


0.8226 


.2 


0.7991 


.3 


0.8734 


.3 


0.8469 


.3 


0.8221 


.3 


0.7986 


.4 


0.8728 


.4 


0.8464 


.4 


0.8216 


.4 


0.7982 


.5 


0.8723 


.5 


0.8459 


.5 


0.8211 


.5 


0.7977 


.6 


0.8717 


.6 


0.8454 


.6 


0.8206 


.6 


0.7973 


.7 


0.8712 


.7 


0.8449 


.7 


0.8202 


.7 


0.7968 


.8 


0.8706 


.8 


0.8444 


.8 


0.8197 


.8 


0.7964 


.9 


0.8701 


.9 


0.8439 


.9 


0.8192 


.9 


0.7959 



606 



THE MODERN ASPHALT PAVEMENT. 



COMPARISON OF ACTUAL SPECIFIC GRAVITY AND DEGREES 
BEAUME HYDROMETER— Continued. 



°B6. 


Sp. Gr. 


° B6. 


Sp. Gr. 


°Bc*. 


Sp. Gr. 


°B<*. 


Sp. Gr. 


46.0 


0.7955 


51.0 


0.7735 


56.0 


0.7527 


61.0 


0.7330 


.1 


0.7950 


.1 


0.7731 


.1 


0.7523 


.1 


0.7326 


.2 


0.7946 


.2 


0.7726 


.2 


0.7519 


.2 


0.7322 


.3 


0.7941 


.3 


0.7722 


.3 


0.7515 


.3 


0.7318 


.4 


0.7937 


.4 


0.7718 


.4 


0.7511 


.4 


0.7315 


.5 


0.7932 


.5 


0.7713 


.5 


0.7507 


.5 


0.7311 


.6 


0.7928 


.6 


0.7709 


.6 


0.7503 


.6 


0*7307 


.7 


0.7923 


.7 


0.7705 


.7 


0.7499 


.7 


0.7303 


.8 


0.7919 


.8 


0.7701 


.8 


0.7495 


.8 


0.7299 


.9 


0.7914 


.9 


0.7697 


.9 


0.7491 


.9 


0.7295 


47.0 


0.7910 


52.0 


0.7692 


57.0 


0.7487 


62.0 


0.7292 


.1 


0.7905 


.1 


0.7688 


.1 


0.7483 


.1 


0.7288 


.2 


0.7901 


.2 


0.7684 


.2 


0.7479 


.2 


0.7284 


.3 


0.7896 


.3 


0.7680 


.3 


0.7475 


.3 


0.7280 


.4 


0.7892 


.4 


0.7675 


.4 


0.7471 


.4 


0.7277 


.5 


0.7887 


.5 


0.7671 


.5 


0.7467 


.5 


0.7273 


.6 


0.7883 


.6 


0.7667 


.6 


0.7463 


.6 


0.7269 


.7 


0.7878 


.7 


0.7663 


.7 


0.7459 


.7 


Z7265 


.8 


0.7874 


.8 


0.7659 


.8 


0.7455 


.8 


0.7261 


.9 


0.?870 


.9 


0.7654 


.9 


0.7451 


.9 


0.7258 


48.0 


0.7865 


53.0 


0.7650 


58.0 


0.7447 


63.0 


0.7254 


.1 


0.7861 


.1 


0.7646 


.1 


0.7443 


.1 


0.7250 


.2 


0.7856 


.2 


0.7642 


.2 


0.7439 


.2 


0.7246 


.3 


0.7852 


.3 


0.7638 


.3 


0.7435 


.3 


0.7243 


.4 


0.7848 


.4 


0.7634 


.4 


0.7431 


.4 


0.7239 


.5 


0.7843 


.5 


0.7629 


.5 


0.7427 


.5 


0.7235 


.6 


0.7839 


.6 


0.7625 


.6 


0.7423 


.6 


0.7231 


.7 


0.7834 


.7 


0.7621 


.7 


0.7419 


.7 


0.7228 


.8 


0.7830 


.8 


0.7617 


.8 


0.7415 


.8 


0.7224 


.9 


0.7826 


.9 


0.7613 


.9 


0.7411 


.9 


0.7220 


49.0 


0.7821 


54.0 


0.7609 


59.0 


0.7407 


64.0 


0.7216 


.1 


0.7817 


.1 


0.7605 


.1 


0.7403 


.1 


0.7213 


.2 


0.7812 


.2 


0.7600 


.2 


6.7400 


.2 


0.7209 


.3 


0.7808 


.3 


0.7596 


.3 


0.7396 


.3 


0.7205 


.4 


0.7804 


.4 


0.7592 


.4 


0.7392 


.4 


0.7202 


.5 


0.7799 


.5 


0.7588 


.5 


0.7388 


.5 


0.7198 


.6 


0.7795 


.6 


0.7584 


.6 


0.7384 


.6 


0.7194 


.7 


0.7791 


.7 


0.7580 
0.7576 


.7 


0.7380 


.7 


0.7191 


.8 


0.7786 


.8 


.8 


0.7376 


.8 


0.7187 


.9 


0.7782 


.9 


0.7572 


.9 


0.7372 


.9 


0.7183 


50.0 


0.7778 


55.0 


0.7568 


60.0 


0.7368 


65.0 


0.7179 


.1 


0.7773 


.1 


0.7563 


.1 


0.7365 


.1 


0.7176 


.2 


0.7769 


.2 


0.7559 


.2 


0.7361 


.2 


0.7172 


.3 


0.7765 


.3 


0.7555 


.3 


0.7357 


.3 


0.7168 


.4 


0.7761 


.4 


0.7551 


.4 


0.7353 


.4 


0.7165 


.5 


0.7756 


.5 


0.7547 


.5 


0.7349 


.5 


0.7161 


.6 


0.7752 


.6 


0.7543 


.6 


0.7345 


.6 


0.7157 


.7 


0.7748 


.7 


0.7539 


.7 


0.7^41 


.7 


0.7154 


.8 


0.7743 


.8 


0.7535 


.8 


0.7338 


.8 


0.7150 


.9 


0.7739 


.9 


0.7531 


.9 


0.7334 


.9 


0.7147 



APPENDIX. 



607 



COMPARISON OF ACTUAL SPECIFIC GRAVITY AND DEGREES 
BEAUM£ HYDROMETER— Continued. 



°B6. 


Sp. Gr. 


°Bc*. 


Sp. Gr. 


°B6. 


Sp. Gr. 


Bd. 


Sp. Gr. 


66.0 


0.7143 


70.0 


0.7000 


74.0 


0.6863 


78.0 


0.6731 


.1 


0.7139 


.1 


0.6997 


.1 


0.6859 


.1 


0.6728 


.2 


0.7136 


.2 


0.6993 


.2 


0.6856 


.2 


0.6724 


.3 


0.7132 


.3 


0.6990 


.3 


0.6853 


.3 


0.6721 


.4 


0.7128 


.4 


0.6986 


.4 


0.6849 


.4 


0.6718 


.5 


0.7125 


.5 


0.6983 


.5 


0.6846 


.5 


0.6715 


.6 


0.7121 


.6 


0.6979 


.6 


0.6843 


.6 


0.6711 


.7 


0.7117 


.7 


0.6976 


.7 


0.6839 


.7 


0.6708 


.8 


0.7114 


.8 


0.6972 


.8 


0.6836 


.8 


0.6705 


.9 


0.7110 


.9 


0.6969 


.9 


0.6833 


.9 


0.6702 


67.0 


0.7107 


71.0 


0.6965 


75.0 


0.6829 


79.0 


0.6699 


.1 


0.7103 


.1 


0.6962 


.1 


0.6826 


.1 


0.6695 


.2 


0.7099 


.2 


0.6958 


.2 


0.6823 


.2 


0.6692 


.3 


0.7096 


.3 


0.6955 


.3 


0.6819 


.3 


0.6689 


.4 


0.7092 


.4 


0.6951 


.4 


0.6816 


.4 


0.6686 


.5 


0.7089 


.5 


0.6948 


.5 


0.6813 


.5 


0.6683 


.6 


0.7085 


.6 


0.6944 


.6 


0.6809 


.6 


0.6679 


.7 


0.7081 


.7 


0.6941 


.7 


0.6806 


.7 


0.6676 


.8 


0.7078 


.8 


0.6938 


.8 


0.6803 


.8 


0.6673 


.9 


0.7074 


.9 


0.6934 


.9 


0.6799 


.9 


0.6670 


168.0 


0.7071 


72.0 


0.6931 


76.0 


0.6796 


80.0 


0.6667 


.1 


0.7067 


.1 


0.6927 


.1 


0.6793 






.2 


0.7064 


.2 


0.6924 


.2 


0.6790 






.3 


0.7060 


.3 


0.6920 


.3 


0.6786 






.4 


0.7056 


.4 


0.6917 


.4 


0.6783 






.5 


0.7053 


.5 


0.6914 


.5 


0.6780 






.6 


0.7049 


.6 


0.6910 


.6 


0.6776 






.7 


0.7046 


.7 


0.6907 


.7 


0.6773 






.8 


0.7042 


.8 


0.6903 


.8 


0.6770 






.9 


0.7039 


.9 


0.6900 


.9 


0.6767 






69.0 


0.7035 


73.0 


0.6897 


77.0 


0.6763 






.1 


0.7032 


.1 


0.6893 


.1 


0.6760 






.2 


0.7028 


.2 


0.6890 


.2 


0.6757 






.3 


0.7025 


.3 


0.6886 


.3 


0.6753 






.4 


0.7021 


.4 


0.6883 


.4 


0.6750 






.5 


0.7018 


.5 


0.6880 


.5 


0.6747 






.6 


0.7014 


.6 


0.6876 


.6 


0.6744 






.7 


0.7011 


.7 


0.6873 


.7 


0.6740 






.8 


0.7007 


.8 


0.6869 


.8 


0.6737 






.9 


0.7004 


.9 


0.6866 


.9 


0.6734 







608 



THE MODERN ASPHALT PAVEMENT. 



FACTORS. 
Metric to U. S. Standard Weight, Measures, etc. 

1 Milligram = .01543 Grain 

1 Gram- = .03572 Ounce (Av'd.) 

1 Kilo = 2.205 Pounds (Av'd.) 



1 Grain 

1 Ounce (Av'd.) 

1 Pound 



64.799 Milligrams 
28.3495 Grams 
.4536 Kilogram 



1 Centimeter 
1 Meter 
1 Meter 
1 Kilometer 



.3937 Inch 

3.281 Feet 

1.0936 Yards 

.6214 Statute mile 



1 Inch 
1 Foot 
1 Yard 
1 Statute mile 



2.540 Centimeters 

.3048 Meter 

.9144 Meter 

1.6093 Kilometers 



1 Liter 
1 Liter 
1 Cubic meter 



- 1.0567 Quarts 
.2647 Gallon 
264.1705 Gallons 



1 Quart 
1 Gallon 
1 Gallon 



.9464 Liter 
3.7854 Liters 
.00379 Cubic meter 



1 Square centimeter 
1 Square meter 
1 Square meter 
1 Square kilometer 

1 Square inch 
1 Square foot 
1 Square yard 
1 Square mile 

1 Cubic centimeter 
1 Cubic meter 
1 Cubic meter 



.1550 Square inch 

10.764 Square Feet 

1.196 Yards 

.3861 Mile 

6.4516 Square centimeters 

.0929 Square meter 

.8361 Square meter 

2.59 Square kilometers 

.06102 Cubic inch 
35.31445 Cubic feet 
1.3079 Cubic yards 



1 Cubic inch 
1 Cubic foot 
1 Cubic yard 

1 Kilogram per square centimeter : 
1 Kilogram per square meter 
1 Kilogram per cubic meter 

1 Pound per square inch •■ 

1 Pound per square foot ■ 

1 Pound per cubic foot 



16.3872 Cubic centimeters 
.02832 Cubic meter 
.76456 Cubic meter 

14.2234 Pounds per square inch 
.20482 Pound per square foot 
.06243 Pound per cubic foot 

.07031 Kilo per square centimeter 
4.8824 Kilos per square meter 
16.0184 Kilos per cubic meter 



1 Gram per 100 cubic centimeter 



.624 Pound per cubic foot 



APPENDIX. 609 

TEMPERATURES CENTIGRADE AND FAHRENHEIT. 





F. 


C. 


F. 


C. 


F. 


C. 


F. 


C. 


F. 


o 


o 


o 


o 


o 


o 


o 


o 


o 


o 


-29 


-20.2 


+39 


+ 102.2 


+ 107 


+ 224.6 


+ 175 


+347.0 


+ 243 


+469.4 


28 


18.4 


40 


104.0 


108 


226.4 


176 


348.8 


244 


471.2 


27 


16.6 


41 


105.8 


109 


228.2 


177 


350.6 


245 


473.0 


26 


14.8 


42 


107.6 


110 


230.0 


178 


352.4 


246 


474.8 


25 


13.0 


43 


109.4 


111 


231.8 


179 


354.2 


247 


476.6 


24 


11.2 


44 


111.2 


112 


233.6 


180 


356.0 


248 


478.4 


23 


9.4 


45 


113.0 


113 


235.4 


181 


357.8 


249 


480.2 


22 


7.6 


46 


114.8 


114 


237.2 


182 


359.6 


250 


482.0 


21 


5.8 


47 


116.6 


115 


239.0 


183 


361.4 


251 


483.8 


20 


4.0 


48 


118.4 


116 


240.8 


184 


363 . 2 


252 


485.6 


19 


2.2 


49 


120.2 


117 


242.6 


185 


365.0 


253 


487.4 


18 


0.4 


50 


122.0 


118 


244.4 


186 


366.8 


254 


489.2 


17 


+ 1.4 


51 


123.8 


119 


246.2 


187 


368.6 


255 


491.0 


16 


3.2 


52 


125.6 


120 


248.0 


188 


370.4 


256 


492.8 


15 


5.0 


53 


127.4 


121 


249.8 


189 


372 . 2 


257 


494.6 


14 


6.8 


54 


129.2 


122 


251.6 


190 


374.0 


258 


496.4 


13 


8.6 


55 


131.0 


123 


253.4 


191 


375.8 


259 


498.2 


12 


10.4 


56 


132.8 


124 


255.2 


192 


377.6 


260 


500.0 


11 


12.2 


57 


134.6 


125 


257.0 


193 


379.4 


261 


501.8 


10 


14.0 


58 


136.4 


126 


258.8 


194 


381.2 


262 


503.6 


9 


15.8 


59 


138.2 


127 


260.6 


195 


383.0 


263 


505.4 


8 


17.6 


60 


140.0 


128 


262.4 


196 


384.8 


264 


507.2 


7 


19.4 


61 


141.8 


129 


264.2 


197 


386.6 


265 


509.0 


6 


21.2 


62 


143.6 


130 


266.0 


198 


388.4 


266 


510.8 


5 


23.0 


63 


145.4 


131 


267.8 


199 


390.2 


267 


512.6 


4 


24.8 


64 


147.2 


132 


269.6 


200 


392.0 


268 


514.4 


3 


26.6 


65 


149.0 


133 


271.4 


201 


393.8 


269 


516.2 


2 


28.4 


66 


150.8 


134 


273.2 


202 


395.6 


270 


518.0 


1 


30.2 


67 


152.6 


135 


275.0 


203 


397.4 


271 


519.8 





32.0 


68 


154.4 


136 


276.8 


204 


399.2 


272 


521.6 


+ 1 


33.8 


69 


156.2 


137 


278.6 


205 


401.0 


273 


523.4 


2 


35.6 


70 


158.0 


138 


280.4 


206 


402.8 


274 


525.2 


3 


37.4 


71 


159.8 


139 


282.2 


207 


404.6 


275 


527.0 


4 


39.2 


72 


161.6 


140 


284.0 


208 


406.4 


276 


528.8 


5 


41.0 


73 


163.4 


141 


285.8 


209 


408.2 


277 


530.6 


6 


42.8 


74 


165.2 


142 


287.6 


210 


410.0 


278 


532.4 


7 


44.6 


75 


167.0 


143 


289.4 


211 


411.8 


279 


534.2 


8 


46.4 


76 


168.8 


144 


291.2 


212 


413.6 


280 


536.0 


9 


48.2 


77 


170.6 


145 


293.0 


213 


415.4 


281 


537.8 


10 


50.0 


78 


172.4 


146 


294.8 


214 


417.2 


282 


539.6 


11 


51.8 


79 


174.2 


147 


296.6 


215 


419.0 


283 


541.4 


12 


53.6 


80 


176.0 


148 


298.4 


216 


420.8 


284 


543.2 


13 


55.4 


81 


177 8 


149 


300.2 


217 


422.6 


285 


545.0 


14 


57.2 


82 


179.6 


150 


302.0 


218 


424.4 


286 


546.8 


15 


59.0 


83 


181.4 


151 


303.8 


219 


426.2 


287 


548.6 


16 


60.8 


84 


183.2 


152 


305.6 


220 


428.0 


288 


550.4 


17 


62.6 


85 


185.0 


153 


307.4 


221 


429.8 


289 


552.2 


18 


64.4 


86 


186.8 


154 


309.2 


222 


431.6 


290 


554.0 


19 


66.2 


87 


„ 188.6 
190.4 


155 


311.0 


223 


433.4 


300 


572.0 


20 


68.0 


88 


156 


312.8 


224 


435.2 


310 


590.0 


21 


69.8 


89 


192.2 


157 


314.6 


225 


437.0 


320 


608.0 


22 


71.6 


90 


194.0 


158 


316.4 


226 


438.8 


330 


626.0 


23 


73.4 


91 


195.8 


159 


318.2 


227 


440.6 


340 


644.0 


24 


75.2 


92 


197.6 


160 


320.0 


228 


442.4 


350 


662.0 


25 


77.0 


93 


199.4 


161 


321.8 


229 


444.2 


360 


680 . 


26 


78.8 


94 


201.2 


162 


323.6 


230 


446.0 


370 


698.0 


27 


80.6 


95 


203.0 


163 


325.4 


231 


447.8 


380 


716.0 


28 


82.4 


96 


204.8 


164 


327.2 


232 


449.6 


390 


734.0 


29 


84.2 


97 


206.6 


165 


329.0 


233 


451.4 


400 


752.0 


30 


86.0 


98 


208.4 


166 


330.8 


234 


453.2 


410 


770.0 


31 


87.8 


99 


210.2 


167 


332.6 


235 


455 . 


420 


788.0 


32 


89.6 


100 


212.0 


168 


334.4 


236 


456 8 


430 


806.0 


33 


91.4 


101 


213.8 


169 


336 . 2 


237 


458 . 6 


440 


824.0 


34 


93.2 


102 


215.6 


170 


338.0 


238 


460.4 


450 


842.0 


35 


95.0 


103 


217.4 


171 


339.8 


239 


462.2 


460 


860.0 


36 


96.8 


104 


219.2 


172 


341.6 


240 


464.0 


470 


878.0 


37 


98.6 


105 


221.0 


173 


343.4 


241 


465.8 


480 1 


896.0 


38 


100.4 


106 

■ 


222.4 


174 


345.2 


242 


467.6 


490 
500 | 


914.0 
932.0 . 



CONCLUSION. 

In closing these pages the author may say that the statements 
which have been made are all founded on his own experience, and 
that the data which have been presented are the result of ex- 
aminations and investigations carried on in his own laboratory, 
except where it is stated to the contrary. The conclusions which 
have been drawn, of course, involve his judgment as well as his 
experience, but they have been based on practical results rather 
than upon theories, as the latter often do not lead to success in the 
construction of asphalt surfaces or to a satisfactory explanation 
of defective work. 

An attempt has been made to gather together such information 
as is available in regard to the asphalt-paving industry and asphalt 
pavements in general, in a form which will appeal to and be under- 
stood by the practical man, the engineer, the asphalt expert and, 
finally, in certain chapters, to the citizen at large. If the result 
proves in any way successful and the character of the asphalt 
pavements which are constructed in the future are in any way 
improved thereby, it will be a sufficient reward for the labor involved 
in bringing out this book. 

610 



INDEX 



Acetone, 591 
Aggregate, mineral, 30 

See also Mineral aggregate 
Albertite, 217 

composition of, 218, 219 
Alcatraz asphalt, 200, 245 
Analysis, methods of, 519 
Appendix, 599 
Ash, determination of, 542 

Asphalt, action of water on, in laboratory, 285, 461, 462 
Alcatraz, 200, 245 
associated with mineral matter, 153 
Bermudez, 178 

crude, extremes in composition of, 183 
hardening of, 181 
refined, 184 

bitumen, ultimate composition, 188 
composition of, 186 
extremes in composition of, 187 
relative per cent of flow of different cargoes, 184 
California, 200 

La Patera, 200 
More Ranch, 202 
other deposits, 206 
Standard, 203 
See also Residual pitches 
Cuban, 192 

"D" grade, physical characteristics and proximate composition of, 
258-260 
specifications for, 263 

611 



612 INDEX. 

Asphalt, defects in asphalt surfaces due to inferiority of, 477 
definition of, 150 
Maracaibo, 190, 191 
Mexico, 194 

Chapapote, 198 
Chijol, 196 

Tamesi river, 194-196 
Tuxpan, 198 
physical properties, determination of, 533 
rock, Continental, 252 
specific heat of, 426 
Texas, 240 

Uvalde County, 240 
Trinidad lake, 156 

bitumen, ultimate composition of, 169 
composition of crude, 160, 163 

refined, 163, 164 
constitution of crude, 160 
extremes in composition of refined, 165 
the bitumen of, 168 

mineral matter in, 161, 165 
land, 171 

average composition of crude, 174 
composition of refined, 176 
extremes in composition of, 177 
use in asphalt surfaces, lack of intelligence in, 477 
Warren's characterization, 150 
Asphalts, Continental rock, 252 

differentiation of, among themselves, 152 

hard, examination of, 530 

individual, 156 

loss on heating, determination of, 534, 554, 555 

native, comparison of their relative merits for paving purposes, 

278 
physical properties of, 533 

and proximate composition of more important, 
148, 149 
refined, examination of, 531 
the, 147 . 
Alphalt-block, 389 

See also Block, asphalt-paving. 
Asphalt cement, amount of residuum necessary in making, 300, 308 
Bermudez, effect of water on, 466 
California, effect of water on, 466 



INDEX. 613 

Asphalt cement, changes in consistency of, on maintaining in a melted con- 
dition, 571 
change in consistency of, with variation of temperature, 309, 

564 
characteristics at different temperatures, when made with 

light and heavy flux, 310 
comparison of consistency of, when made with different 

fluxes, 301 
consistency, determination of, 558 
determination of composition of, 569, 571 

susceptibility to changes in temperature of, 
564 
ductility, see Ductility 
examination of, 558 
gilsonite, 211, 280, 306 
ductility, 211 
grahamite, ductility of, 213 
pneumatic lift for, 404 
the character of various, 296 
preparation of, 293 
Asphalt cements, composition of those made with paraffine and asphaltie 
fluxes and various asphalts, 297, 308 
containing blown oil, 307 
effect of filler on ductility, 373 
made from residual pitches, 307 

with asphaltie flux, composition of, 297, 303 
natural malthas, 304 
paraffine residuum, 296 
physical properties of, 308 
stability at high temperature, 301, 571 
Asphalt pavement, merits of, 455 
Asphalt pavements, action of water on, 460 

on the street, 461, 495 
illuminating-gas on, 491-494 
causes of the defects in and deterioration of, 471 
cost of, 457 

maintenance of, 458 
grades suitable for, 450 
maintenance of, 445, 458, 504 
specifications for, see Specifications 
See also Asphalt surfaces 
Asphalt surfaces, absorption of water by, 465, 468 
contraction of, 425 
cracking of, 480 



614 INDEX. 

Asphalt surfaces, defects in, 471 

See also Defects 
deterioration of, 471 

due to environment, 499-502 

expansion of cement in foundation, 

499 
natural wear, 502 
neglect of maintenance, 502 
disintegration of, 490 

due to, 490 

action of illuminating-gas, 491-494 
inferior mixture, 491 
poor workmanship, 496 
water action, 461, 495 
displacement of, 498 
effect of climate on, 484 

radiation, expansion, contraction, and resistance to im- 
pact, 425 
scaling of, 497 
strength of, 485-490 
See also Surface mixture 
Asphaltenes, 121, 122 
Asphaltic or bituminous concrete, 348, 375 

binder, 25, 388 
examination of, 576 

See also Concrete, asphaltic or bituminous 
limestones, 221 

American, characteristics of, 238 
Continental, 252 
Oklahoma, 232, 238 
Texas, 240 
Utah, 248 
sands, 221 

bitumen impregnating, 224, 228 
California, 243 

Carpinteria, 246 
San Luis Obispo, 244 
Santa Barbara, 245 
Santa Cruz, 243 
Kentucky, 221 

importance of, 229 
Oklahoma, 230-239 
Texas, 240 
Utah, 248 



INDEX. 615 

Balance, Chaslyn, 574 

sand, 523 
Base or foundation, see Foundation 
Beaume degrees and specific gravity, 604 
Bermudez asphalt, see Asphalt 

asphalt cement, effect of water on, 466 
Binder, analysis of close or compact, 26 
asphaltic concrete, 25, 388 

consistency of asphalt cement in use in, 23, 439 
course, 21 

placing on street, 413 
specifications for close or compact, 439 
open, 438 
of Kansas City, Mo., 599 
3itumen, amount of, which sands and mineral aggregates will carry, 351 
determination of, in surface mixtures, 571 
insoluble in carbon tetrachloride, 124 
in surface mixtures before 1896, 319 
litho-carbon, 241 

naphtha soluble, determination of, 542 
pure, preparation of, 547, 548 
soluble in carbon disulphide, 123 

tetrachloride, 546 
specific heat of, 426 

total, determination of, in asphalts, 540 
Bitumens, identification of, 586 

native, characterization and classification of, 11© 
differentiation of, 115 
in use in the paving industry, 115 
physical properties of, 115 
solid, chemical characteristics of, 121 
color of powder or streak, 119 
fixed carbon in, 122, 125 
flowing of, 120 
fracture of, 120 
hardness of, 120 
lustre of, 119 
odor of, 120 
softening of, 120 
specific gravity of, 117 
structure of, 119 
solid, 147 

native, not asphalt, 208 

the product of condensation of heavy oils, 272 



616 INDEX. 

Bituminous macadam, see Concrete, asphaltic or bituminous 
Block, asphalt-paving, 389 

analysis of various manufacturers', 393 
method of, 576 

components entering into composition of, 390 
Blown oil in asphalt cement, 307 

Bulletin No. 1, Barber Asphalt Paving Companyi March, 1896, 322 
Byerlyte, 273 

California asphalt, see Asphalt 

asphaltic sands in, 243-246 
See also Asphaltic sands 
California oil asphalt cement, effect of water on, 466 
Camber, suitable for asphalt streets, 451 
Carbenes, 122, 124, 546 
Carbon disulphide, 590 

bitumen soluble in, 123 
fixed, 122, 125 

determination of, 549 
tetrachloride, 590 

bitumen insoluble in, 124, 546 
Cement, asphalt, examination of, 558 
curb, 446 

expansion of, in foundation, 499 
hydraulic, character of, 13 
Centrifugal method for examination of asphaltic or bituminous concrete and 

asphalt paving blocks, 576 
surface mixtures, 573 
Chicago, surface mixtures, 1898 and 1899, produced without technical super- 
vision, 337 
Chloroform, 589 

Clay soils, specifications for the construction of asphalt pavements on, 448 
Climate, effect of, on asphalt surfaces, 484 
Color of powder or streak of bitumen, 119 
Colorado, bitumen in, 246 
Conclusion, 610 
Concrete, asphaltic or bituminous, 348, 375-388 

analysis of, 380, 381, 383 
production of, 386 

plant for, 407 
specifications for, 441 
See also Asphaltic or bituminous concrete, 
coal tar, 378, 379 

Evans' pavement, Washington, D. C, laid in 1873, 375 



INDEX. 617 

Continental asphaltic limestones, 252 

Contraction of asphalt surfaces, 425 

Cracking of asphalt surfaces, 480 m 

Crown, formulas for, for streets of different width, 452, 453 

suitable for asphalt streets, 451 
Crusher screenings, 12 
Cuban asphalt, see Asphalt 
Curb, cement, 446 
Cushion coat, 19-21 
Cyclic hydrocarbons, 103 

Cylinders, table for determining the cubic contents of, 582 

surface of, 584 

Defects in asphalt surfaces, causes of, 471 

due to careless workmanship, 477 
character of filler, 476 
improper specifications, 472 
inferior sand, 324, 327, 474 
inferiority in the asphalt or lack of intelli- 
gence in its use, 477 
lack of lateral support, 15, 473 
manner in which they are manifested, 479 
Density, determination of, in surface mixtures, 580 

See also Specific gravity 
Deterioration in asphalt surfaces, causes of, 471 

See also Asphalt surfaces 
Determination of bitumen in surface mixture, 571 

insoluble in carbon tetrachloride, 546 
character of filler, 529 
composition of asphalt cement, 569-571 
consistency of asphalt cement, 559 
density and voids in surface mixture, 580 
flash-point, 554 

insoluble matter, or difference, 123 
loss on heating asphalts, or fluxes, 534, 554 
mineral matter or ash, 542 
naphtha soluble bitumen, 542 
paraffine scale, 556- 558 
physical properties of asphalt, 533 
melting or flowing points, 538 
sand grading, 521, 526 
specific gravity, 552 
viscosity, 551 
voids in sands and mineral aggregates, 526 



618 INDEX. 

Determination of volume weight of sand, 528 

water absorption by surface mixtures, 583 
See also Examination 
Dow, A. W., 491, 495, 559 
Drainage, 4, 5 

of clay soils, 448 
Drum, sand, 396, 401 

Ductility of asphalt cement, effect of filler on^ 373 
gilsonite asphalt cement, 211 
grahamite asphalt cement, 213 
Dust, see Filler 

Ebano asphalt, see Residual pitch 
Elutriation test, see Filler 
Examination of asphalt blocks, 576 
cement, 558 
asphaltic concrete, 576 
hard asphalts, 530 
refined asphalt, 531 
surface mixture, 571 

by centrifugal method, 573 
stone, gravel, slag, etc., 519 
See also Determination of 
Expansion, coefficient of, of materials in use in asphalt surface mixture, 481 
of asphalt surfaces, 427 

coefficient of, 481, 483 
Ether, 591 

Filler, 87 

defects in asphalt surfaces due to inferiority of, 476 

determination and character of, 529 

of character of, by elutriation method, 92, 529 

effect of, on ductility of asphalt cement, 373 

method of examining, 92, 529 

number of particles and square feet of surface in one pound of New 
York filler, 359 

portion of 200-mesh material acting as, 346, 348, 349, 364 

role played by, in preventing water action, 373 

size of particles in, 94 

volume weight of, 94 
Fixed carbon, see Carbon 
Flash-point, determination of, 554 

Flint, crushed, weight per cubic foot and voids compared with those in 
sand, 83 



INDEX. 619 

Flow-test, 567-569 

Flowing of native solid bitumens, 115 
Flux, amount of, necessary in making asphalt cement, 300 
asphaltic, 136 

comparison of asphalt cements made with, 297 
Beaumont, Texas, 141 

or similar, 141 

specifications for, 142 
California, "G" grade, 136-139 

defects in, 139 
specifications for, 139 
comparison of, consistency of asphalt cements at different temperatures 

when made with different fluxes, 301 
light and heavy, characteristics of asphalt cements made with, at 

different temperatures, 311 
parafnne, composition of asphalt cements made with, 297 
Pittsburg, 272 

Texas, Beaumont, and similar, 141 
Ventura, 272 
See also Residuum 
Fluxes, 127 

examination of, 550 

loss on heating, determination of, 534, 554, 555 
Formulas for crowns of streets of different width, 452, 453 
Foundation, or base, 3 

bituminous, 6 

expansion of cement in, 499 
granite block, 8 
hydraulic concrete, 9 
old brick pavement, 8 
macadam, 7 
subsoil, 4 
Fracture of solid native bitumens, 120 

Gas, illuminating, action on asphalt surfaces, 491-494 

composition of, 493 
Gilsonite, 208 

asphalt cement, ductility oi, 210, 211, 280 

composition of, 208 

in use. in the paving industry 211, 288 
Glance-pitch, 213 

composition of, 215 
Grades suitable for asphalt pavements, 450 
Grading, comparison of different sands having the same, 361 



620 INDEX. 

Grading, extension of, when containing much coarser and much finer parti 
cles than the standard, 347 
of sands, 84 

determination of, 521-526 
in various cities, with and without filler, 362 
standard, 332, 342 
Grahamite, 192, 211 

asphalt cement, ductility of, 213 
composition of, 212, 214 
in use in the paving industry, 213 
Oklahoma, 239 
Grains, number of, in one gram of sand of uniform diameter, 358 
Granite blocks, foundation, 7 
Gravel in conrcete base, 9, 11, 437 
Gutters for asphalt streets, 453 

Hardness of native solid bitumens, 120 

Heat, absorption and radiation of, by various pavements, 425-427 

specific, of asphalt, 426 
Heaters, sand, 396, 401 

surface, for use in repairs to asphalt pavements, 507 
Heating, asphalts and fluxes, determination of loss on, 534, 554 
Horses' feet, effect of, on asphalt pavement, 428 
Hydrocarbons, chain, 98 

cyclic, 103 

unsaturated, 104 

derivatives, 108 

dicyclic, 105 

native, 98 

olefine, 102 

paraffine, 101 

poly cyclic, 106 

polymethylene, 103, 106 

saturated, 99 

unsaturated, 102 
Hydrolene"B," 273 

Impact tests of asphalt surface mixture, 287, 428 

method of making, 585 
Identification of bitumens, 586 
Indianapolis, Ind., defective surface mixture, 337 
Inorganic matter, 123 
Intermediate course, 19 



INDEX. 621 



Kentucky asphaltic sands, see Asphaltic sands 

bituminous sands, 221-229 
Kettles, see Tanks 

Laboratory equipment, 595 

Lateral support, defects in asphalt surfaces due to, 15, 473 

Lift, pneumatic, for asphalt cement, 404 

Limestones, asphaltic, 221 

American, 238 

Continental, 252 

Oklahoma, 232-238 
Litho-carbon bitumen, 241 
London, England, surface mixture, 328 
Lustre of native solid bitumens, 119 



Macadam as a foundation, 7 

bituminous, see Concrete, asphaltic or bituminous 
Machinery for producing asphalt surface mixture, 400 
Maintenance, cost of, of asphalt pavements, 458, 504 
due to natural wear, 502 
of asphalt pavements, 445, 458, 504 
Maltha as a flux, 304 
Malthas, 127 

natural, asphalt cements made with, 304 
Malthenes, 121, 124 

determination of character of, 544 
in asphalts, 542 
Manjak, 213 

composition of, 216 
Maracaibo asphalt, see Asphalt 

Materials, instructions for collecting samples of, 509 

Measures and weights, table for converting metric to U. S. standards, 608 
Melting-tanks, 398, 404 
Merits of asphalt pavement, 455 

asphalts for paving purposes, opinion of Western chemist on, 281 
various asphalts for paving purposes, 276 
Methods of analysis, 519 
Mexico, asphalt, see Asphalt 
Mineral aggregate, 30 

1892-1899, 317-319 

amount of bitumen which it will carry, 351 
extension of grading of, when containing much coarser 
and much finer particles than the standard, 347 



622 INDEX. 

Mineral aggregate, voids in, method of determining, 526 
See also Sand 
matter associated with asphalt, 153 
determination of, 542 
in Trinidad lake asphalt, 165 
Mixer for making surface mixture and binder, 406 
Mixture, surface, see Surface mixture 

Naphthas, 592 

Naphtha soluble bitumen, determination of, 542 

New York defective surface mixtures, 325, 326, 338 

mixtures produced in, with inferior sand grading, 338, 475 

Odor of native solid bitumens, 120 
Oils, blown, 273 

in asphalt cements, 307 
Oklahoma, asphaltic limestones, 232, 234, 238 
sands, 230-239 

deposits of bitumen, 230 

grahamite, 239 

value of the bituminous deposits of, for paving purposes, 240 
Omaha surface mixtures, 322 
Oven employed in author's laboratory, 535-538 
Ozocerite, 217 

Paint-coat, 27 

specifications for, 28 
Parafrme scale, determination of, 556-558 

in residuum, 134 
Particles, size of, passed by sieves, 59 
Pat paper test, 352-356 

method of making, 514, 515 
Paving industry, bitumens in use in, 115 
Penetration machines, 559-567 

Bo wen, 559 
Dow. 559 

New York Testing Laboratory, 565 
Petrolenes, 121 

Petroleum, classification of, 112 
Petroleums, 127 
Pitch, residual, asphalt cements made from, 307 

differentiation of, from natural asphalt, 276 
from California petroleum, 256 
Kansas petroleum, 273 



INDEX. 623 

Pitch, residual, from Mexican petroleum, 270 

petroleum, 256 

Russian petroleum, 270, 271 

Texas petroleum, 266 

See also Residual pitch 
Pittsburg flux, 272 

Plant, for production of bituminous concrete, 407 
Plants, permanent, 400 

portable and semi-portable, 406 
types of, 400 
Polymethylene hydrocarbons, 103, 106 
Powder, color of, 119 
Pyro- bitumens, 111, 217 
Physical properties of asphalt, 533 

Radiation of various pavements, 425-427 
Rakes, proper type of, 417 
Raking surface mixture, 417-419 
Refining of solid bitumens, 291 

tanks, 404 
Residual pitch, asphalt cements containing, as an amendment, 307 

made from, 306 
characteristics of, 256-277 
from Kansas petroleum (Sarco), 273 
Mexican petroleum (Ebano), 270 
Texas petroleum, 266 
See also Pitch, residual 
Repairs to asphalt pavements, cost of, in Washington, D. C, 458, 504 

use of surface heaters in making, 507 
Residuum, asphaltic, asphalt cements made with, 296 

characteristics of asphalt cements at different temperatures when 

made with light and heavy, 311 
complete solubility of asphalt in, 299 
examination of, 550 
paramne, character of, 131-136 
petroleum, 131 
scale in, 134 
specifications for, 134 
suitability for use as a flux, 296 
petroleum, 127 

California asphaltic, 136 

character of, 137 
specifications for, 139 
Kansas, 135 



624 INDEX. 

Residuum, shale oil, 144 

Texas, 141 

specifications for, 142 

See also Flux 
Rollers, 419, 420 

Samples, instructions for collecting, 509 
Sampling, methods to be employed in, 512 
Sand, 30 

100- and 80-mesh, role played in preventing water action, 373 

See also Sand, fine 
amount of bitumen it will carry, 351 
average per cent of 200-mesh in, from various cities» 364 
balance, 523 
bituminous, California, 243 

Carpinteria, 246 
San Luis Obispo, 244 
Santa Barbara, 245 
Santa Cruz, 243 
classification of, 32 
concrete, 11 

defects in asphalt surfaces due to inferior grade, 474 
effect of 200-mesh, on surface mixture, 345 
fine, defects of, in surface mixtures, 323, 324, 328, 332, 334, 338-342, 

344, 345 
grading, extension when containing much coarser and much finer 

particles than the standard, 347 
grading, in different cities, with and without filler, 362 
lack of sand for obtaining standard, 339 
mixture produced in New York City with improper, 337, 475 
grains, shape of, 56 

size of, 59, 60 
heaters, 396, 401 
New York, weight and voids in, with various percentages of 200-mesh 

dust, 82 
number of particles in one pound of mineral aggregate, New York, 1895 

and 1898, 359 
number of particles in one gram of grains of uniform diameter, 358 
sharp as compared with round, 84 
square feet of surface of one pound, New York mineral aggregate, 1895 

and 1898, 359 
standard grading, 332, 342 

for light traffic, 342 
voids in, 72, 526 



INDEX. 625 

Sand, volume weight of, determination of, 528 

weight and voids in New York sand with various percentages of 200- 
mesh dust, 82 

See also Mineral aggregate 
Sands, alluvial, 39 

artificial, 52 

asphaltic, 221 

Kentucky, 221 

bitumen impregnating, 224, 228 
importance of, 229 

See also Asphaltic sands 

bank or pit, 46 

comparison of different, having the same grading, 361 

composition of, 53 

determination of the grading of, 521 

glacial, 51 

grading of, 84 

determination of, 521-526 

pounds per cubic foot and voids in various, 78, 81 

lakeshore, 36 

of different composition having the same grading, 361 

purchase of, 53 

quick, 48 

river, 39 

seabeach, 34 

sieves for sifting, 59 

sifting of, 59 

specific gravity of, 363 

surface of, 57 

voids, see Sands, weight per cubic foot 

volume weight of hot, per cubic foot, 82 

weight per cubic foot and voids in the average, from various cities, 
with filler to make 200-mesh material equal to 15 per cent, 365, 366 

weight per cubic foot and voids in New York sand with and without 
dust, compared with the same grading of sands from other cities, 363 

weight per cubic foot and voids of, compared with those in crushed 
flint, 83 

weight per cubic foot of, 77 
Sandy soils, 449 
Sarco, see Residual pitch 
Scaling of asphalt surfaces, 497 
Screenings, crusher, 12 
Sieves, manufacture of, 61 

method of using, 522, 525 



626 INDEX. 

Sieves, uniformity of, 59 

for mechanical sifting, 524 
Sifting of sand, 59 

Softening of native solid bitumens, 120 
Soils, clay, 4 

specifications for construction of asphalt pavements on, 448 
sandy, 449 
Solvents, 589 
Specific gravity, determination of, 552 

of native solid bitumens, 117 

oils or fluxes, method of determining, in use in Chicago 

City laboratory, 552 
sands, 363 

surface mixtures, 367 
Specific heat of asphalt, 426 
Specifications, 435 

clay soils, 4, 448 

defects in asphalt surfaces due to improper, 472 

for asphalt pavements, 435 

Kansas City, Mo., 599 
asphaltic concrete, 441 
compact or close binder, 439 
"D" grade asphalt, 263 
"G" grade California flux, 139 
open binder, 438 
paraffine residuum, 134 
Texas or similar oil, 142 
St. Louis surface mixture, 327 
Standard grading, 332, 342 
Stone block pavement as foundation, 6, 7 
Stone, examination of, 519 
Street, construction work on, 413 
railroad tracks, 16 
transportation of materials to, 412 
Structure of native solid bitumens, 119 
Subsoil, 4 

Sulphuric acid, action on hydrocarbons, 102, 124 
Support, lateral, 15, 473 
Surface course, placing on street, 415 

heaters, use of, in repairing asphalt pavements, 507 
mixture, 313 

Bermudez, destruction of, by water, 463 

effect of three months' action by water, 465 
capacity for absorbing water, 369-372 



INDEX. 627 

Surface mixture, characteristics, indicative of the properties of, old and new, 
367 
defects in, 471 

due to inferiority of asphalt, 477 
density of, 367 
determination of bitumen in, 571 

density and voids in, 580 
examination of, 571 

by centrifugal method, 573 
impact tests of, 287, 428 

materials in use in, coefficient of expansion of, 481 
on rule of thumb basis, 336 
points for consideration in a standard, 332 
process of combining the constituents into, 395 
raking of, 417-419 
sampling of, 514 
standard, 332, 342 

why it is satisfactory, 371 
Trinidad lake asphalt, effect of three months' action on, by 

water, 465 
See also Asphalt surfaces 
Surface mixtures, action of water on, on the street, 461 
average composition before 1894, 314 

in 1897, 321 
Barber Asphalt Paving Company, 1896-1899 and 1904, 

329-331 
bitumen in, before 1889-1899, 319, 320 
Chicago, 1898, 1899, produced without technical super- 
vision, 337 
coarser than standard, 339 
composition of, before 1894, 314 
defective, Indianapolis, Ind., 337 
Toronto, Canada, 337 
Utica, N. Y., 337 
effect of 200-mesh sand on, 345 
grading of sand in, before 1894, 316 
London, England, 1896, 328 
made with fine sand, 323, 324, 328, 332, 334, 337, 339-342, 

344, 345 
method of making impact tests, 585 
mushy, 349 

New York, defective, 1895, 325, 326, 338 
Omaha, average bitumen in good, medium, and badly 
cracked surfaces, 322 



628 INDEX. 

Surface mixtures, produced in New York City in 1904 without proper super- 
vision of sand grading, 338, 475 
without technical supervision in Chicago in 1898 
and 1899, 337 
St. Louis, 1892 and 1893, 327 
standard grading for light traffic, 342 
Washington, D. C., 1896, 327 
water absorption of, 583 



Tanks, melting, 398, 404 

steam melting, 404 
Technology of the paving industry, 291 

Temperature, changes in consistency of asphalt cement with variations of, 
309, 564 
conversion of Centigrade to Fahrenheit readings, 609 
different, characterization of asphalt cement when made with 

light and heavy fluxes, at, 311 
high, stability of asphalt cements at, 301, 571 
proper, for surface mixture, 415, 416 
susceptibility of asphalt cement to changes in, 564 
Test, pat paper, see Pat paper test 
Texas, asphaltic limestones, 240 
sands, 240 
asphalts, see Asphalts 
Tools for use on street, 422 

Toronto, Canada, defective surface mixture, 337 
Traffic, 484 

and lack of it, effect on asphalt surfaces, 484 
en asphalt pavements in New York City, 457 
Transportation of materials to the street, 412 
Trinidad asphalt, see Asphalt 
Turpentine, oil of, 590 

Utah, asphaltic sands, see Asphaltic sands 

bituminous sands and limestones, 248 

native bitumens of, 247 

See also Gilsonite, Wurztilite, and Ozocerite 
Utica, N. Y., defective surface mixture, 337 

Ventura flux, 272 
Vibration of rails, 16 
Viscosity, determination of, 554 



INDEX. 629 

Voids, as affected by size and shape of particles and by their uniformity, 77 
determination of, in sand, 75 

surface mixture, 580 
in mineral aggregates, determination of, 526 
sand, 72 
Volume weight of filler, 94 

sand, determination of, 528 
sands, hot, per cubic foot, 82 
Washington, D. C, cost of repairs to asphalt pavements in, 458, 505 

surface mixture, 327 
Water absorption, capacity of surface mixture for, 369, 372 

cause of action of, on asphalt under certain circumstances, 

467 
by Trinidad and Bermudez surface mixtures, pounds per 

square yard, 465 
of surface mixtures, 583 
action of, on asphalt pavements, 460 

in the laboratory, 285, 461, 462 
surfaces, 495 
actual results of action of, on asphalt surface mixtures on^the street, 

461 
comparison of action of, on surface mixtures in the laboratory and on 

the street, 462, 466 
effect on Bermudez asphalt cement, 466 

California oil asphalt cements, 466 
relative absorption of, by coarse and fine asphalt surface mixtures, 468 
Wax tailings, 143-145 

Weights and measures, table for converting metric to U. S. standards, 608 
Whipple & Jackson, asphalts, action of water on, 461 
Work, control of, 509 

inspection of, 509 
Workmanship, careless, defects in asphalt surfaces due to, 477 

poor, disintegration of asphalt surfaces, due to, 496 
Wurtzilite, 218 

composition of, 220 



. 







